Google Git
Sign in
fuchsia / third_party / rust / 10732e14f4ee6e462170f883c79fb90acf3ddc2c / . / library / core / src / fmt / mod.rs
blob: 580f95eddce7119a6aa910279bb2ada4a74949d5 [file] [log] [blame]
//! Utilities for formatting and printing strings.
#![stable(feature = "rust1", since = "1.0.0")]
use crate::cell::{Cell, Ref, RefCell, RefMut, SyncUnsafeCell, UnsafeCell};
use crate::char::{EscapeDebugExtArgs, MAX_LEN_UTF8};
use crate::marker::PhantomData;
use crate::num::fmt as numfmt;
use crate::ops::Deref;
use crate::{iter, result, str};
mod builders;
#[cfg(not(no_fp_fmt_parse))]
mod float;
#[cfg(no_fp_fmt_parse)]
mod nofloat;
mod num;
mod rt;
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
#[rustc_diagnostic_item = "Alignment"]
/// Possible alignments returned by `Formatter::align`
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Alignment {
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be left-aligned.
Left,
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be right-aligned.
Right,
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
/// Indication that contents should be center-aligned.
Center,
}
#[stable(feature = "debug_builders", since = "1.2.0")]
pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
#[unstable(feature = "debug_closure_helpers", issue = "117729")]
pub use self::builders::{FromFn, from_fn};
/// The type returned by formatter methods.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// #[derive(Debug)]
/// struct Triangle {
/// a: f32,
/// b: f32,
/// c: f32
/// }
///
/// impl fmt::Display for Triangle {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {}, {})", self.a, self.b, self.c)
/// }
/// }
///
/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
///
/// assert_eq!(format!("{pythagorean_triple}"), "(3, 4, 5)");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub type Result = result::Result<(), Error>;
/// The error type which is returned from formatting a message into a stream.
///
/// This type does not support transmission of an error other than that an error
/// occurred. This is because, despite the existence of this error,
/// string formatting is considered an infallible operation.
/// `fmt()` implementors should not return this `Error` unless they received it from their
/// [`Formatter`]. The only time your code should create a new instance of this
/// error is when implementing `fmt::Write`, in order to cancel the formatting operation when
/// writing to the underlying stream fails.
///
/// Any extra information must be arranged to be transmitted through some other means,
/// such as storing it in a field to be consulted after the formatting operation has been
/// cancelled. (For example, this is how [`std::io::Write::write_fmt()`] propagates IO errors
/// during writing.)
///
/// This type, `fmt::Error`, should not be
/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
/// have in scope.
///
/// [`std::io::Error`]: ../../std/io/struct.Error.html
/// [`std::io::Write::write_fmt()`]: ../../std/io/trait.Write.html#method.write_fmt
/// [`std::error::Error`]: ../../std/error/trait.Error.html
///
/// # Examples
///
/// ```rust
/// use std::fmt::{self, write};
///
/// let mut output = String::new();
/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
/// panic!("An error occurred");
/// }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Error;
/// A trait for writing or formatting into Unicode-accepting buffers or streams.
///
/// This trait only accepts UTF-8–encoded data and is not [flushable]. If you only
/// want to accept Unicode and you don't need flushing, you should implement this trait;
/// otherwise you should implement [`std::io::Write`].
///
/// [`std::io::Write`]: ../../std/io/trait.Write.html
/// [flushable]: ../../std/io/trait.Write.html#tymethod.flush
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Write {
/// Writes a string slice into this writer, returning whether the write
/// succeeded.
///
/// This method can only succeed if the entire string slice was successfully
/// written, and this method will not return until all data has been
/// written or an error occurs.
///
/// # Errors
///
/// This function will return an instance of [`std::fmt::Error`][Error] on error.
///
/// The purpose of that error is to abort the formatting operation when the underlying
/// destination encounters some error preventing it from accepting more text;
/// in particular, it does not communicate any information about *what* error occurred.
/// It should generally be propagated rather than handled, at least when implementing
/// formatting traits.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
/// f.write_str(s)
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, "hola")?;
/// assert_eq!(&buf, "hola");
/// # std::fmt::Result::Ok(())
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn write_str(&mut self, s: &str) -> Result;
/// Writes a [`char`] into this writer, returning whether the write succeeded.
///
/// A single [`char`] may be encoded as more than one byte.
/// This method can only succeed if the entire byte sequence was successfully
/// written, and this method will not return until all data has been
/// written or an error occurs.
///
/// # Errors
///
/// This function will return an instance of [`Error`] on error.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
/// f.write_char(c)
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, 'a')?;
/// writer(&mut buf, 'b')?;
/// assert_eq!(&buf, "ab");
/// # std::fmt::Result::Ok(())
/// ```
#[stable(feature = "fmt_write_char", since = "1.1.0")]
fn write_char(&mut self, c: char) -> Result {
self.write_str(c.encode_utf8(&mut [0; MAX_LEN_UTF8]))
}
/// Glue for usage of the [`write!`] macro with implementors of this trait.
///
/// This method should generally not be invoked manually, but rather through
/// the [`write!`] macro itself.
///
/// # Errors
///
/// This function will return an instance of [`Error`] on error. Please see
/// [write_str](Write::write_str) for details.
///
/// # Examples
///
/// ```
/// use std::fmt::{Error, Write};
///
/// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
/// f.write_fmt(format_args!("{s}"))
/// }
///
/// let mut buf = String::new();
/// writer(&mut buf, "world")?;
/// assert_eq!(&buf, "world");
/// # std::fmt::Result::Ok(())
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
// We use a specialization for `Sized` types to avoid an indirection
// through `&mut self`
trait SpecWriteFmt {
fn spec_write_fmt(self, args: Arguments<'_>) -> Result;
}
impl<W: Write + ?Sized> SpecWriteFmt for &mut W {
#[inline]
default fn spec_write_fmt(mut self, args: Arguments<'_>) -> Result {
if let Some(s) = args.as_statically_known_str() {
self.write_str(s)
} else {
write(&mut self, args)
}
}
}
impl<W: Write> SpecWriteFmt for &mut W {
#[inline]
fn spec_write_fmt(self, args: Arguments<'_>) -> Result {
if let Some(s) = args.as_statically_known_str() {
self.write_str(s)
} else {
write(self, args)
}
}
}
self.spec_write_fmt(args)
}
}
#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
impl<W: Write + ?Sized> Write for &mut W {
fn write_str(&mut self, s: &str) -> Result {
(**self).write_str(s)
}
fn write_char(&mut self, c: char) -> Result {
(**self).write_char(c)
}
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
(**self).write_fmt(args)
}
}
/// The signedness of a [`Formatter`] (or of a [`FormattingOptions`]).
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[unstable(feature = "formatting_options", issue = "118117")]
pub enum Sign {
/// Represents the `+` flag.
Plus,
/// Represents the `-` flag.
Minus,
}
/// Specifies whether the [`Debug`] trait should use lower-/upper-case
/// hexadecimal or normal integers.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[unstable(feature = "formatting_options", issue = "118117")]
pub enum DebugAsHex {
/// Use lower-case hexadecimal integers for the `Debug` trait (like [the `x?` type](../../std/fmt/index.html#formatting-traits)).
Lower,
/// Use upper-case hexadecimal integers for the `Debug` trait (like [the `X?` type](../../std/fmt/index.html#formatting-traits)).
Upper,
}
/// Options for formatting.
///
/// `FormattingOptions` is a [`Formatter`] without an attached [`Write`] trait.
/// It is mainly used to construct `Formatter` instances.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[unstable(feature = "formatting_options", issue = "118117")]
pub struct FormattingOptions {
/// Flags, with the following bit fields:
///
/// ```text
/// 31 30 29 28 27 26 25 24 23 22 21 20 0
/// ┌───┬───────┬───┬───┬───┬───┬───┬───┬───┬───┬──────────────────────────────────┐
/// │ 1 │ align │ p │ w │ X?│ x?│'0'│ # │ - │ + │ fill │
/// └───┴───────┴───┴───┴───┴───┴───┴───┴───┴───┴──────────────────────────────────┘
/// │ │ │ │ └─┬───────────────────┘ └─┬──────────────────────────────┘
/// │ │ │ │ │ └─ The fill character (21 bits char).
/// │ │ │ │ └─ The debug upper/lower hex, zero pad, alternate, and plus/minus flags.
/// │ │ │ └─ Whether a width is set. (The value is stored separately.)
/// │ │ └─ Whether a precision is set. (The value is stored separately.)
/// │ ├─ 0: Align left. (<)
/// │ ├─ 1: Align right. (>)
/// │ ├─ 2: Align center. (^)
/// │ └─ 3: Alignment not set. (default)
/// └─ Always set.
/// This makes it possible to distinguish formatting flags from
/// a &str size when stored in (the upper bits of) the same field.
/// (fmt::Arguments will make use of this property in the future.)
/// ```
// Note: This could use a special niche type with range 0x8000_0000..=0xfdd0ffff.
// It's unclear if that's useful, though.
flags: u32,
/// Width if width flag (bit 27) above is set. Otherwise, always 0.
width: u16,
/// Precision if precision flag (bit 28) above is set. Otherwise, always 0.
precision: u16,
}
// This needs to match with compiler/rustc_ast_lowering/src/format.rs.
mod flags {
pub(super) const SIGN_PLUS_FLAG: u32 = 1 << 21;
pub(super) const SIGN_MINUS_FLAG: u32 = 1 << 22;
pub(super) const ALTERNATE_FLAG: u32 = 1 << 23;
pub(super) const SIGN_AWARE_ZERO_PAD_FLAG: u32 = 1 << 24;
pub(super) const DEBUG_LOWER_HEX_FLAG: u32 = 1 << 25;
pub(super) const DEBUG_UPPER_HEX_FLAG: u32 = 1 << 26;
pub(super) const WIDTH_FLAG: u32 = 1 << 27;
pub(super) const PRECISION_FLAG: u32 = 1 << 28;
pub(super) const ALIGN_BITS: u32 = 0b11 << 29;
pub(super) const ALIGN_LEFT: u32 = 0 << 29;
pub(super) const ALIGN_RIGHT: u32 = 1 << 29;
pub(super) const ALIGN_CENTER: u32 = 2 << 29;
pub(super) const ALIGN_UNKNOWN: u32 = 3 << 29;
pub(super) const ALWAYS_SET: u32 = 1 << 31;
}
impl FormattingOptions {
/// Construct a new `FormatterBuilder` with the supplied `Write` trait
/// object for output that is equivalent to the `{}` formatting
/// specifier:
///
/// - no flags,
/// - filled with spaces,
/// - no alignment,
/// - no width,
/// - no precision, and
/// - no [`DebugAsHex`] output mode.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn new() -> Self {
Self {
flags: ' ' as u32 | flags::ALIGN_UNKNOWN | flags::ALWAYS_SET,
width: 0,
precision: 0,
}
}
/// Sets or removes the sign (the `+` or the `-` flag).
///
/// - `+`: This is intended for numeric types and indicates that the sign
/// should always be printed. By default only the negative sign of signed
/// values is printed, and the sign of positive or unsigned values is
/// omitted. This flag indicates that the correct sign (+ or -) should
/// always be printed.
/// - `-`: Currently not used
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn sign(&mut self, sign: Option<Sign>) -> &mut Self {
let sign = match sign {
None => 0,
Some(Sign::Plus) => flags::SIGN_PLUS_FLAG,
Some(Sign::Minus) => flags::SIGN_MINUS_FLAG,
};
self.flags = self.flags & !(flags::SIGN_PLUS_FLAG | flags::SIGN_MINUS_FLAG) | sign;
self
}
/// Sets or unsets the `0` flag.
///
/// This is used to indicate for integer formats that the padding to width should both be done with a 0 character as well as be sign-aware
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn sign_aware_zero_pad(&mut self, sign_aware_zero_pad: bool) -> &mut Self {
if sign_aware_zero_pad {
self.flags |= flags::SIGN_AWARE_ZERO_PAD_FLAG;
} else {
self.flags &= !flags::SIGN_AWARE_ZERO_PAD_FLAG;
}
self
}
/// Sets or unsets the `#` flag.
///
/// This flag indicates that the "alternate" form of printing should be
/// used. The alternate forms are:
/// - [`Debug`] : pretty-print the [`Debug`] formatting (adds linebreaks and indentation)
/// - [`LowerHex`] as well as [`UpperHex`] - precedes the argument with a `0x`
/// - [`Octal`] - precedes the argument with a `0b`
/// - [`Binary`] - precedes the argument with a `0o`
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn alternate(&mut self, alternate: bool) -> &mut Self {
if alternate {
self.flags |= flags::ALTERNATE_FLAG;
} else {
self.flags &= !flags::ALTERNATE_FLAG;
}
self
}
/// Sets the fill character.
///
/// The optional fill character and alignment is provided normally in
/// conjunction with the width parameter. This indicates that if the value
/// being formatted is smaller than width some extra characters will be
/// printed around it.
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn fill(&mut self, fill: char) -> &mut Self {
self.flags = self.flags & (u32::MAX << 21) | fill as u32;
self
}
/// Sets or removes the alignment.
///
/// The alignment specifies how the value being formatted should be
/// positioned if it is smaller than the width of the formatter.
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn align(&mut self, align: Option<Alignment>) -> &mut Self {
let align: u32 = match align {
Some(Alignment::Left) => flags::ALIGN_LEFT,
Some(Alignment::Right) => flags::ALIGN_RIGHT,
Some(Alignment::Center) => flags::ALIGN_CENTER,
None => flags::ALIGN_UNKNOWN,
};
self.flags = self.flags & !flags::ALIGN_BITS | align;
self
}
/// Sets or removes the width.
///
/// This is a parameter for the “minimum width” that the format should take
/// up. If the value’s string does not fill up this many characters, then
/// the padding specified by [`FormattingOptions::fill`]/[`FormattingOptions::align`]
/// will be used to take up the required space.
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn width(&mut self, width: Option<u16>) -> &mut Self {
if let Some(width) = width {
self.flags |= flags::WIDTH_FLAG;
self.width = width;
} else {
self.flags &= !flags::WIDTH_FLAG;
self.width = 0;
}
self
}
/// Sets or removes the precision.
///
/// - For non-numeric types, this can be considered a “maximum width”. If
/// the resulting string is longer than this width, then it is truncated
/// down to this many characters and that truncated value is emitted with
/// proper fill, alignment and width if those parameters are set.
/// - For integral types, this is ignored.
/// - For floating-point types, this indicates how many digits after the
/// decimal point should be printed.
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn precision(&mut self, precision: Option<u16>) -> &mut Self {
if let Some(precision) = precision {
self.flags |= flags::PRECISION_FLAG;
self.precision = precision;
} else {
self.flags &= !flags::PRECISION_FLAG;
self.precision = 0;
}
self
}
/// Specifies whether the [`Debug`] trait should use lower-/upper-case
/// hexadecimal or normal integers
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn debug_as_hex(&mut self, debug_as_hex: Option<DebugAsHex>) -> &mut Self {
let debug_as_hex = match debug_as_hex {
None => 0,
Some(DebugAsHex::Lower) => flags::DEBUG_LOWER_HEX_FLAG,
Some(DebugAsHex::Upper) => flags::DEBUG_UPPER_HEX_FLAG,
};
self.flags = self.flags & !(flags::DEBUG_LOWER_HEX_FLAG | flags::DEBUG_UPPER_HEX_FLAG)
| debug_as_hex;
self
}
/// Returns the current sign (the `+` or the `-` flag).
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_sign(&self) -> Option<Sign> {
if self.flags & flags::SIGN_PLUS_FLAG != 0 {
Some(Sign::Plus)
} else if self.flags & flags::SIGN_MINUS_FLAG != 0 {
Some(Sign::Minus)
} else {
None
}
}
/// Returns the current `0` flag.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_sign_aware_zero_pad(&self) -> bool {
self.flags & flags::SIGN_AWARE_ZERO_PAD_FLAG != 0
}
/// Returns the current `#` flag.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_alternate(&self) -> bool {
self.flags & flags::ALTERNATE_FLAG != 0
}
/// Returns the current fill character.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_fill(&self) -> char {
// SAFETY: We only ever put a valid `char` in the lower 21 bits of the flags field.
unsafe { char::from_u32_unchecked(self.flags & 0x1FFFFF) }
}
/// Returns the current alignment.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_align(&self) -> Option<Alignment> {
match self.flags & flags::ALIGN_BITS {
flags::ALIGN_LEFT => Some(Alignment::Left),
flags::ALIGN_RIGHT => Some(Alignment::Right),
flags::ALIGN_CENTER => Some(Alignment::Center),
_ => None,
}
}
/// Returns the current width.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_width(&self) -> Option<u16> {
if self.flags & flags::WIDTH_FLAG != 0 { Some(self.width) } else { None }
}
/// Returns the current precision.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_precision(&self) -> Option<u16> {
if self.flags & flags::PRECISION_FLAG != 0 { Some(self.precision) } else { None }
}
/// Returns the current precision.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn get_debug_as_hex(&self) -> Option<DebugAsHex> {
if self.flags & flags::DEBUG_LOWER_HEX_FLAG != 0 {
Some(DebugAsHex::Lower)
} else if self.flags & flags::DEBUG_UPPER_HEX_FLAG != 0 {
Some(DebugAsHex::Upper)
} else {
None
}
}
/// Creates a [`Formatter`] that writes its output to the given [`Write`] trait.
///
/// You may alternatively use [`Formatter::new()`].
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn create_formatter<'a>(self, write: &'a mut (dyn Write + 'a)) -> Formatter<'a> {
Formatter { options: self, buf: write }
}
}
#[unstable(feature = "formatting_options", issue = "118117")]
impl Default for FormattingOptions {
/// Same as [`FormattingOptions::new()`].
fn default() -> Self {
// The `#[derive(Default)]` implementation would set `fill` to `\0` instead of space.
Self::new()
}
}
/// Configuration for formatting.
///
/// A `Formatter` represents various options related to formatting. Users do not
/// construct `Formatter`s directly; a mutable reference to one is passed to
/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
///
/// To interact with a `Formatter`, you'll call various methods to change the
/// various options related to formatting. For examples, please see the
/// documentation of the methods defined on `Formatter` below.
#[allow(missing_debug_implementations)]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Formatter"]
pub struct Formatter<'a> {
options: FormattingOptions,
buf: &'a mut (dyn Write + 'a),
}
impl<'a> Formatter<'a> {
/// Creates a new formatter with given [`FormattingOptions`].
///
/// If `write` is a reference to a formatter, it is recommended to use
/// [`Formatter::with_options`] instead as this can borrow the underlying
/// `write`, thereby bypassing one layer of indirection.
///
/// You may alternatively use [`FormattingOptions::create_formatter()`].
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn new(write: &'a mut (dyn Write + 'a), options: FormattingOptions) -> Self {
Formatter { options, buf: write }
}
/// Creates a new formatter based on this one with given [`FormattingOptions`].
#[unstable(feature = "formatting_options", issue = "118117")]
pub fn with_options<'b>(&'b mut self, options: FormattingOptions) -> Formatter<'b> {
Formatter { options, buf: self.buf }
}
}
/// This structure represents a safely precompiled version of a format string
/// and its arguments. This cannot be generated at runtime because it cannot
/// safely be done, so no constructors are given and the fields are private
/// to prevent modification.
///
/// The [`format_args!`] macro will safely create an instance of this structure.
/// The macro validates the format string at compile-time so usage of the
/// [`write()`] and [`format()`] functions can be safely performed.
///
/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
/// and `Display` contexts as seen below. The example also shows that `Debug`
/// and `Display` format to the same thing: the interpolated format string
/// in `format_args!`.
///
/// ```rust
/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
/// assert_eq!("1 foo 2", display);
/// assert_eq!(display, debug);
/// ```
///
/// [`format()`]: ../../std/fmt/fn.format.html
#[lang = "format_arguments"]
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Copy, Clone)]
pub struct Arguments<'a> {
// Format string pieces to print.
pieces: &'a [&'static str],
// Placeholder specs, or `None` if all specs are default (as in "{}{}").
fmt: Option<&'a [rt::Placeholder]>,
// Dynamic arguments for interpolation, to be interleaved with string
// pieces. (Every argument is preceded by a string piece.)
args: &'a [rt::Argument<'a>],
}
/// Used by the format_args!() macro to create a fmt::Arguments object.
#[doc(hidden)]
#[unstable(feature = "fmt_internals", issue = "none")]
impl<'a> Arguments<'a> {
#[inline]
pub const fn new_const<const N: usize>(pieces: &'a [&'static str; N]) -> Self {
const { assert!(N <= 1) };
Arguments { pieces, fmt: None, args: &[] }
}
/// When using the format_args!() macro, this function is used to generate the
/// Arguments structure.
#[inline]
pub const fn new_v1<const P: usize, const A: usize>(
pieces: &'a [&'static str; P],
args: &'a [rt::Argument<'a>; A],
) -> Arguments<'a> {
const { assert!(P >= A && P <= A + 1, "invalid args") }
Arguments { pieces, fmt: None, args }
}
/// Specifies nonstandard formatting parameters.
///
/// An `rt::UnsafeArg` is required because the following invariants must be held
/// in order for this function to be safe:
/// 1. The `pieces` slice must be at least as long as `fmt`.
/// 2. Every `rt::Placeholder::position` value within `fmt` must be a valid index of `args`.
/// 3. Every `rt::Count::Param` within `fmt` must contain a valid index of `args`.
#[inline]
pub const fn new_v1_formatted(
pieces: &'a [&'static str],
args: &'a [rt::Argument<'a>],
fmt: &'a [rt::Placeholder],
_unsafe_arg: rt::UnsafeArg,
) -> Arguments<'a> {
Arguments { pieces, fmt: Some(fmt), args }
}
/// Estimates the length of the formatted text.
///
/// This is intended to be used for setting initial `String` capacity
/// when using `format!`. Note: this is neither the lower nor upper bound.
#[inline]
pub fn estimated_capacity(&self) -> usize {
let pieces_length: usize = self.pieces.iter().map(|x| x.len()).sum();
if self.args.is_empty() {
pieces_length
} else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
// If the format string starts with an argument,
// don't preallocate anything, unless length
// of pieces is significant.
0
} else {
// There are some arguments, so any additional push
// will reallocate the string. To avoid that,
// we're "pre-doubling" the capacity here.
pieces_length.checked_mul(2).unwrap_or(0)
}
}
}
impl<'a> Arguments<'a> {
/// Gets the formatted string, if it has no arguments to be formatted at runtime.
///
/// This can be used to avoid allocations in some cases.
///
/// # Guarantees
///
/// For `format_args!("just a literal")`, this function is guaranteed to
/// return `Some("just a literal")`.
///
/// For most cases with placeholders, this function will return `None`.
///
/// However, the compiler may perform optimizations that can cause this
/// function to return `Some(_)` even if the format string contains
/// placeholders. For example, `format_args!("Hello, {}!", "world")` may be
/// optimized to `format_args!("Hello, world!")`, such that `as_str()`
/// returns `Some("Hello, world!")`.
///
/// The behavior for anything but the trivial case (without placeholders)
/// is not guaranteed, and should not be relied upon for anything other
/// than optimization.
///
/// # Examples
///
/// ```rust
/// use std::fmt::Arguments;
///
/// fn write_str(_: &str) { /* ... */ }
///
/// fn write_fmt(args: &Arguments<'_>) {
/// if let Some(s) = args.as_str() {
/// write_str(s)
/// } else {
/// write_str(&args.to_string());
/// }
/// }
/// ```
///
/// ```rust
/// assert_eq!(format_args!("hello").as_str(), Some("hello"));
/// assert_eq!(format_args!("").as_str(), Some(""));
/// assert_eq!(format_args!("{:?}", std::env::current_dir()).as_str(), None);
/// ```
#[stable(feature = "fmt_as_str", since = "1.52.0")]
#[rustc_const_stable(feature = "const_arguments_as_str", since = "1.84.0")]
#[must_use]
#[inline]
pub const fn as_str(&self) -> Option<&'static str> {
match (self.pieces, self.args) {
([], []) => Some(""),
([s], []) => Some(s),
_ => None,
}
}
/// Same as [`Arguments::as_str`], but will only return `Some(s)` if it can be determined at compile time.
#[unstable(feature = "fmt_internals", reason = "internal to standard library", issue = "none")]
#[must_use]
#[inline]
#[doc(hidden)]
pub fn as_statically_known_str(&self) -> Option<&'static str> {
let s = self.as_str();
if core::intrinsics::is_val_statically_known(s.is_some()) { s } else { None }
}
}
// Manually implementing these results in better error messages.
#[stable(feature = "rust1", since = "1.0.0")]
impl !Send for Arguments<'_> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl !Sync for Arguments<'_> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for Arguments<'_> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
Display::fmt(self, fmt)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Arguments<'_> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
write(fmt.buf, *self)
}
}
/// `?` formatting.
///
/// `Debug` should format the output in a programmer-facing, debugging context.
///
/// Generally speaking, you should just `derive` a `Debug` implementation.
///
/// When used with the alternate format specifier `#?`, the output is pretty-printed.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
/// comma-separated list of each field's name and `Debug` value, then `}`. For
/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
/// `Debug` values of the fields, then `)`.
///
/// # Stability
///
/// Derived `Debug` formats are not stable, and so may change with future Rust
/// versions. Additionally, `Debug` implementations of types provided by the
/// standard library (`std`, `core`, `alloc`, etc.) are not stable, and
/// may also change with future Rust versions.
///
/// # Examples
///
/// Deriving an implementation:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(
/// format!("The origin is: {origin:?}"),
/// "The origin is: Point { x: 0, y: 0 }",
/// );
/// ```
///
/// Manually implementing:
///
/// ```
/// use std::fmt;
///
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// impl fmt::Debug for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// f.debug_struct("Point")
/// .field("x", &self.x)
/// .field("y", &self.y)
/// .finish()
/// }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(
/// format!("The origin is: {origin:?}"),
/// "The origin is: Point { x: 0, y: 0 }",
/// );
/// ```
///
/// There are a number of helper methods on the [`Formatter`] struct to help you with manual
/// implementations, such as [`debug_struct`].
///
/// [`debug_struct`]: Formatter::debug_struct
///
/// Types that do not wish to use the standard suite of debug representations
/// provided by the `Formatter` trait (`debug_struct`, `debug_tuple`,
/// `debug_list`, `debug_set`, `debug_map`) can do something totally custom by
/// manually writing an arbitrary representation to the `Formatter`.
///
/// ```
/// # use std::fmt;
/// # struct Point {
/// # x: i32,
/// # y: i32,
/// # }
/// #
/// impl fmt::Debug for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "Point [{} {}]", self.x, self.y)
/// }
/// }
/// ```
///
/// `Debug` implementations using either `derive` or the debug builder API
/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
///
/// Pretty-printing with `#?`:
///
/// ```
/// #[derive(Debug)]
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// let expected = "The origin is: Point {
/// x: 0,
/// y: 0,
/// }";
/// assert_eq!(format!("The origin is: {origin:#?}"), expected);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_on_unimplemented(
on(
crate_local,
label = "`{Self}` cannot be formatted using `{{:?}}`",
note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {Debug} for {Self}`"
),
message = "`{Self}` doesn't implement `{Debug}`",
label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`"
)]
#[doc(alias = "{:?}")]
#[rustc_diagnostic_item = "Debug"]
#[rustc_trivial_field_reads]
pub trait Debug {
#[doc = include_str!("fmt_trait_method_doc.md")]
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Position {
/// longitude: f32,
/// latitude: f32,
/// }
///
/// impl fmt::Debug for Position {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// f.debug_tuple("")
/// .field(&self.longitude)
/// .field(&self.latitude)
/// .finish()
/// }
/// }
///
/// let position = Position { longitude: 1.987, latitude: 2.983 };
/// assert_eq!(format!("{position:?}"), "(1.987, 2.983)");
///
/// assert_eq!(format!("{position:#?}"), "(
/// 1.987,
/// 2.983,
/// )");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
pub(crate) mod macros {
/// Derive macro generating an impl of the trait `Debug`.
#[rustc_builtin_macro]
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
pub macro Debug($item:item) {
/* compiler built-in */
}
}
#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
#[doc(inline)]
pub use macros::Debug;
/// Format trait for an empty format, `{}`.
///
/// Implementing this trait for a type will automatically implement the
/// [`ToString`][tostring] trait for the type, allowing the usage
/// of the [`.to_string()`][tostring_function] method. Prefer implementing
/// the `Display` trait for a type, rather than [`ToString`][tostring].
///
/// `Display` is similar to [`Debug`], but `Display` is for user-facing
/// output, and so cannot be derived.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
/// [tostring]: ../../std/string/trait.ToString.html
/// [tostring_function]: ../../std/string/trait.ToString.html#tymethod.to_string
///
/// # Internationalization
///
/// Because a type can only have one `Display` implementation, it is often preferable
/// to only implement `Display` when there is a single most "obvious" way that
/// values can be formatted as text. This could mean formatting according to the
/// "invariant" culture and "undefined" locale, or it could mean that the type
/// display is designed for a specific culture/locale, such as developer logs.
///
/// If not all values have a justifiably canonical textual format or if you want
/// to support alternative formats not covered by the standard set of possible
/// [formatting traits], the most flexible approach is display adapters: methods
/// like [`str::escape_default`] or [`Path::display`] which create a wrapper
/// implementing `Display` to output the specific display format.
///
/// [formatting traits]: ../../std/fmt/index.html#formatting-traits
/// [`Path::display`]: ../../std/path/struct.Path.html#method.display
///
/// # Examples
///
/// Implementing `Display` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
/// impl fmt::Display for Point {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {})", self.x, self.y)
/// }
/// }
///
/// let origin = Point { x: 0, y: 0 };
///
/// assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");
/// ```
#[rustc_on_unimplemented(
on(
any(_Self = "std::path::Path", _Self = "std::path::PathBuf"),
label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
as they may contain non-Unicode data"
),
message = "`{Self}` doesn't implement `{Display}`",
label = "`{Self}` cannot be formatted with the default formatter",
note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
)]
#[doc(alias = "{}")]
#[rustc_diagnostic_item = "Display"]
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Display {
#[doc = include_str!("fmt_trait_method_doc.md")]
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Position {
/// longitude: f32,
/// latitude: f32,
/// }
///
/// impl fmt::Display for Position {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// write!(f, "({}, {})", self.longitude, self.latitude)
/// }
/// }
///
/// assert_eq!(
/// "(1.987, 2.983)",
/// format!("{}", Position { longitude: 1.987, latitude: 2.983, }),
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `o` formatting.
///
/// The `Octal` trait should format its output as a number in base-8.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0o` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let x = 42; // 42 is '52' in octal
///
/// assert_eq!(format!("{x:o}"), "52");
/// assert_eq!(format!("{x:#o}"), "0o52");
///
/// assert_eq!(format!("{:o}", -16), "37777777760");
/// ```
///
/// Implementing `Octal` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Octal for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::Octal::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(9);
///
/// assert_eq!(format!("l as octal is: {l:o}"), "l as octal is: 11");
///
/// assert_eq!(format!("l as octal is: {l:#06o}"), "l as octal is: 0o0011");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Octal {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `b` formatting.
///
/// The `Binary` trait should format its output as a number in binary.
///
/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0b` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with [`i32`]:
///
/// ```
/// let x = 42; // 42 is '101010' in binary
///
/// assert_eq!(format!("{x:b}"), "101010");
/// assert_eq!(format!("{x:#b}"), "0b101010");
///
/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
/// ```
///
/// Implementing `Binary` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Binary for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::Binary::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(107);
///
/// assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");
///
/// assert_eq!(
/// // Note that the `0b` prefix added by `#` is included in the total width, so we
/// // need to add two to correctly display all 32 bits.
/// format!("l as binary is: {l:#034b}"),
/// "l as binary is: 0b00000000000000000000000001101011"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Binary {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `x` formatting.
///
/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
/// in lower case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let y = 42; // 42 is '2a' in hex
///
/// assert_eq!(format!("{y:x}"), "2a");
/// assert_eq!(format!("{y:#x}"), "0x2a");
///
/// assert_eq!(format!("{:x}", -16), "fffffff0");
/// ```
///
/// Implementing `LowerHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerHex for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(9);
///
/// assert_eq!(format!("l as hex is: {l:x}"), "l as hex is: 9");
///
/// assert_eq!(format!("l as hex is: {l:#010x}"), "l as hex is: 0x00000009");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerHex {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `X` formatting.
///
/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
/// in upper case.
///
/// For primitive signed integers (`i8` to `i128`, and `isize`),
/// negative values are formatted as the two’s complement representation.
///
/// The alternate flag, `#`, adds a `0x` in front of the output.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `i32`:
///
/// ```
/// let y = 42; // 42 is '2A' in hex
///
/// assert_eq!(format!("{y:X}"), "2A");
/// assert_eq!(format!("{y:#X}"), "0x2A");
///
/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
/// ```
///
/// Implementing `UpperHex` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperHex for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = self.0;
///
/// fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
/// }
/// }
///
/// let l = Length(i32::MAX);
///
/// assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");
///
/// assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperHex {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `p` formatting.
///
/// The `Pointer` trait should format its output as a memory location. This is commonly presented
/// as hexadecimal. For more information on formatters, see [the module-level documentation][module].
///
/// Printing of pointers is not a reliable way to discover how Rust programs are implemented.
/// The act of reading an address changes the program itself, and may change how the data is represented
/// in memory, and may affect which optimizations are applied to the code.
///
/// The printed pointer values are not guaranteed to be stable nor unique identifiers of objects.
/// Rust allows moving values to different memory locations, and may reuse the same memory locations
/// for different purposes.
///
/// There is no guarantee that the printed value can be converted back to a pointer.
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `&i32`:
///
/// ```
/// let x = &42;
///
/// let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'
/// ```
///
/// Implementing `Pointer` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::Pointer for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// // use `as` to convert to a `*const T`, which implements Pointer, which we can use
///
/// let ptr = self as *const Self;
/// fmt::Pointer::fmt(&ptr, f)
/// }
/// }
///
/// let l = Length(42);
///
/// println!("l is in memory here: {l:p}");
///
/// let l_ptr = format!("{l:018p}");
/// assert_eq!(l_ptr.len(), 18);
/// assert_eq!(&l_ptr[..2], "0x");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Pointer"]
pub trait Pointer {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `e` formatting.
///
/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
///
/// assert_eq!(format!("{x:e}"), "4.2e1");
/// ```
///
/// Implementing `LowerExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::LowerExp for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = f64::from(self.0);
/// fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
/// }
/// }
///
/// let l = Length(100);
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:e}"),
/// "l in scientific notation is: 1e2"
/// );
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:05e}"),
/// "l in scientific notation is: 001e2"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait LowerExp {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// `E` formatting.
///
/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
///
/// For more information on formatters, see [the module-level documentation][module].
///
/// [module]: ../../std/fmt/index.html
///
/// # Examples
///
/// Basic usage with `f64`:
///
/// ```
/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
///
/// assert_eq!(format!("{x:E}"), "4.2E1");
/// ```
///
/// Implementing `UpperExp` on a type:
///
/// ```
/// use std::fmt;
///
/// struct Length(i32);
///
/// impl fmt::UpperExp for Length {
/// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let val = f64::from(self.0);
/// fmt::UpperExp::fmt(&val, f) // delegate to f64's implementation
/// }
/// }
///
/// let l = Length(100);
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:E}"),
/// "l in scientific notation is: 1E2"
/// );
///
/// assert_eq!(
/// format!("l in scientific notation is: {l:05E}"),
/// "l in scientific notation is: 001E2"
/// );
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub trait UpperExp {
#[doc = include_str!("fmt_trait_method_doc.md")]
#[stable(feature = "rust1", since = "1.0.0")]
fn fmt(&self, f: &mut Formatter<'_>) -> Result;
}
/// Takes an output stream and an `Arguments` struct that can be precompiled with
/// the `format_args!` macro.
///
/// The arguments will be formatted according to the specified format string
/// into the output stream provided.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use std::fmt;
///
/// let mut output = String::new();
/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
/// .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// Please note that using [`write!`] might be preferable. Example:
///
/// ```
/// use std::fmt::Write;
///
/// let mut output = String::new();
/// write!(&mut output, "Hello {}!", "world")
/// .expect("Error occurred while trying to write in String");
/// assert_eq!(output, "Hello world!");
/// ```
///
/// [`write!`]: crate::write!
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
let mut formatter = Formatter::new(output, FormattingOptions::new());
let mut idx = 0;
match args.fmt {
None => {
// We can use default formatting parameters for all arguments.
for (i, arg) in args.args.iter().enumerate() {
// SAFETY: args.args and args.pieces come from the same Arguments,
// which guarantees the indexes are always within bounds.
let piece = unsafe { args.pieces.get_unchecked(i) };
if !piece.is_empty() {
formatter.buf.write_str(*piece)?;
}
// SAFETY: There are no formatting parameters and hence no
// count arguments.
unsafe {
arg.fmt(&mut formatter)?;
}
idx += 1;
}
}
Some(fmt) => {
// Every spec has a corresponding argument that is preceded by
// a string piece.
for (i, arg) in fmt.iter().enumerate() {
// SAFETY: fmt and args.pieces come from the same Arguments,
// which guarantees the indexes are always within bounds.
let piece = unsafe { args.pieces.get_unchecked(i) };
if !piece.is_empty() {
formatter.buf.write_str(*piece)?;
}
// SAFETY: arg and args.args come from the same Arguments,
// which guarantees the indexes are always within bounds.
unsafe { run(&mut formatter, arg, args.args) }?;
idx += 1;
}
}
}
// There can be only one trailing string piece left.
if let Some(piece) = args.pieces.get(idx) {
formatter.buf.write_str(*piece)?;
}
Ok(())
}
unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::Placeholder, args: &[rt::Argument<'_>]) -> Result {
let (width, precision) =
// SAFETY: arg and args come from the same Arguments,
// which guarantees the indexes are always within bounds.
unsafe { (getcount(args, &arg.width), getcount(args, &arg.precision)) };
let options = FormattingOptions { flags: arg.flags, width, precision };
// Extract the correct argument
debug_assert!(arg.position < args.len());
// SAFETY: arg and args come from the same Arguments,
// which guarantees its index is always within bounds.
let value = unsafe { args.get_unchecked(arg.position) };
// Set all the formatting options.
fmt.options = options;
// Then actually do some printing
// SAFETY: this is a placeholder argument.
unsafe { value.fmt(fmt) }
}
unsafe fn getcount(args: &[rt::Argument<'_>], cnt: &rt::Count) -> u16 {
match *cnt {
rt::Count::Is(n) => n,
rt::Count::Implied => 0,
rt::Count::Param(i) => {
debug_assert!(i < args.len());
// SAFETY: cnt and args come from the same Arguments,
// which guarantees this index is always within bounds.
unsafe { args.get_unchecked(i).as_u16().unwrap_unchecked() }
}
}
}
/// Padding after the end of something. Returned by `Formatter::padding`.
#[must_use = "don't forget to write the post padding"]
pub(crate) struct PostPadding {
fill: char,
padding: u16,
}
impl PostPadding {
fn new(fill: char, padding: u16) -> PostPadding {
PostPadding { fill, padding }
}
/// Writes this post padding.
pub(crate) fn write(self, f: &mut Formatter<'_>) -> Result {
for _ in 0..self.padding {
f.buf.write_char(self.fill)?;
}
Ok(())
}
}
impl<'a> Formatter<'a> {
fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
where
'b: 'c,
F: FnOnce(&'b mut (dyn Write + 'b)) -> &'c mut (dyn Write + 'c),
{
Formatter {
// We want to change this
buf: wrap(self.buf),
// And preserve these
options: self.options,
}
}
// Helper methods used for padding and processing formatting arguments that
// all formatting traits can use.
/// Performs the correct padding for an integer which has already been
/// emitted into a str. The str should *not* contain the sign for the
/// integer, that will be added by this method.
///
/// # Arguments
///
/// * is_nonnegative - whether the original integer was either positive or zero.
/// * prefix - if the '#' character (Alternate) is provided, this
/// is the prefix to put in front of the number.
/// * buf - the byte array that the number has been formatted into
///
/// This function will correctly account for the flags provided as well as
/// the minimum width. It will not take precision into account.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo { nb: i32 }
///
/// impl Foo {
/// fn new(nb: i32) -> Foo {
/// Foo {
/// nb,
/// }
/// }
/// }
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// // We need to remove "-" from the number output.
/// let tmp = self.nb.abs().to_string();
///
/// formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
/// }
/// }
///
/// assert_eq!(format!("{}", Foo::new(2)), "2");
/// assert_eq!(format!("{}", Foo::new(-1)), "-1");
/// assert_eq!(format!("{}", Foo::new(0)), "0");
/// assert_eq!(format!("{:#}", Foo::new(-1)), "-Foo 1");
/// assert_eq!(format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
let mut width = buf.len();
let mut sign = None;
if !is_nonnegative {
sign = Some('-');
width += 1;
} else if self.sign_plus() {
sign = Some('+');
width += 1;
}
let prefix = if self.alternate() {
width += prefix.chars().count();
Some(prefix)
} else {
None
};
// Writes the sign if it exists, and then the prefix if it was requested
#[inline(never)]
fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
if let Some(c) = sign {
f.buf.write_char(c)?;
}
if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) }
}
// The `width` field is more of a `min-width` parameter at this point.
let min = self.options.width;
if width >= usize::from(min) {
// We're over the minimum width, so then we can just write the bytes.
write_prefix(self, sign, prefix)?;
self.buf.write_str(buf)
} else if self.sign_aware_zero_pad() {
// The sign and prefix goes before the padding if the fill character
// is zero
let old_options = self.options;
self.options.fill('0').align(Some(Alignment::Right));
write_prefix(self, sign, prefix)?;
let post_padding = self.padding(min - width as u16, Alignment::Right)?;
self.buf.write_str(buf)?;
post_padding.write(self)?;
self.options = old_options;
Ok(())
} else {
// Otherwise, the sign and prefix goes after the padding
let post_padding = self.padding(min - width as u16, Alignment::Right)?;
write_prefix(self, sign, prefix)?;
self.buf.write_str(buf)?;
post_padding.write(self)
}
}
/// Takes a string slice and emits it to the internal buffer after applying
/// the relevant formatting flags specified.
///
/// The flags recognized for generic strings are:
///
/// * width - the minimum width of what to emit
/// * fill/align - what to emit and where to emit it if the string
/// provided needs to be padded
/// * precision - the maximum length to emit, the string is truncated if it
/// is longer than this length
///
/// Notably this function ignores the `flag` parameters.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// formatter.pad("Foo")
/// }
/// }
///
/// assert_eq!(format!("{Foo:<4}"), "Foo ");
/// assert_eq!(format!("{Foo:0>4}"), "0Foo");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn pad(&mut self, s: &str) -> Result {
// Make sure there's a fast path up front.
if self.options.flags & (flags::WIDTH_FLAG | flags::PRECISION_FLAG) == 0 {
return self.buf.write_str(s);
}
// The `precision` field can be interpreted as a maximum width for the
// string being formatted.
let (s, char_count) = if let Some(max_char_count) = self.options.get_precision() {
let mut iter = s.char_indices();
let remaining = match iter.advance_by(usize::from(max_char_count)) {
Ok(()) => 0,
Err(remaining) => remaining.get(),
};
// SAFETY: The offset of `.char_indices()` is guaranteed to be
// in-bounds and between character boundaries.
let truncated = unsafe { s.get_unchecked(..iter.offset()) };
(truncated, usize::from(max_char_count) - remaining)
} else {
// Use the optimized char counting algorithm for the full string.
(s, s.chars().count())
};
// The `width` field is more of a minimum width parameter at this point.
if char_count < usize::from(self.options.width) {
// If we're under the minimum width, then fill up the minimum width
// with the specified string + some alignment.
let post_padding =
self.padding(self.options.width - char_count as u16, Alignment::Left)?;
self.buf.write_str(s)?;
post_padding.write(self)
} else {
// If we're over the minimum width or there is no minimum width, we
// can just emit the string.
self.buf.write_str(s)
}
}
/// Writes the pre-padding and returns the unwritten post-padding.
///
/// Callers are responsible for ensuring post-padding is written after the
/// thing that is being padded.
pub(crate) fn padding(
&mut self,
padding: u16,
default: Alignment,
) -> result::Result<PostPadding, Error> {
let align = self.options.get_align().unwrap_or(default);
let fill = self.options.get_fill();
let padding_left = match align {
Alignment::Left => 0,
Alignment::Right => padding,
Alignment::Center => padding / 2,
};
for _ in 0..padding_left {
self.buf.write_char(fill)?;
}
Ok(PostPadding::new(fill, padding - padding_left))
}
/// Takes the formatted parts and applies the padding.
///
/// Assumes that the caller already has rendered the parts with required precision,
/// so that `self.precision` can be ignored.
///
/// # Safety
///
/// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
unsafe fn pad_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
if self.options.width == 0 {
// this is the common case and we take a shortcut
// SAFETY: Per the precondition.
unsafe { self.write_formatted_parts(formatted) }
} else {
// for the sign-aware zero padding, we render the sign first and
// behave as if we had no sign from the beginning.
let mut formatted = formatted.clone();
let mut width = self.options.width;
let old_options = self.options;
if self.sign_aware_zero_pad() {
// a sign always goes first
let sign = formatted.sign;
self.buf.write_str(sign)?;
// remove the sign from the formatted parts
formatted.sign = "";
width = width.saturating_sub(sign.len() as u16);
self.options.fill('0').align(Some(Alignment::Right));
}
// remaining parts go through the ordinary padding process.
let len = formatted.len();
let ret = if usize::from(width) <= len {
// no padding
// SAFETY: Per the precondition.
unsafe { self.write_formatted_parts(&formatted) }
} else {
let post_padding = self.padding(width - len as u16, Alignment::Right)?;
// SAFETY: Per the precondition.
unsafe {
self.write_formatted_parts(&formatted)?;
}
post_padding.write(self)
};
self.options = old_options;
ret
}
}
/// # Safety
///
/// Any `numfmt::Part::Copy` parts in `formatted` must contain valid UTF-8.
unsafe fn write_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
unsafe fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
// SAFETY: This is used for `numfmt::Part::Num` and `numfmt::Part::Copy`.
// It's safe to use for `numfmt::Part::Num` since every char `c` is between
// `b'0'` and `b'9'`, which means `s` is valid UTF-8. It's safe to use for
// `numfmt::Part::Copy` due to this function's precondition.
buf.write_str(unsafe { str::from_utf8_unchecked(s) })
}
if !formatted.sign.is_empty() {
self.buf.write_str(formatted.sign)?;
}
for part in formatted.parts {
match *part {
numfmt::Part::Zero(mut nzeroes) => {
const ZEROES: &str = // 64 zeroes
"0000000000000000000000000000000000000000000000000000000000000000";
while nzeroes > ZEROES.len() {
self.buf.write_str(ZEROES)?;
nzeroes -= ZEROES.len();
}
if nzeroes > 0 {
self.buf.write_str(&ZEROES[..nzeroes])?;
}
}
numfmt::Part::Num(mut v) => {
let mut s = [0; 5];
let len = part.len();
for c in s[..len].iter_mut().rev() {
*c = b'0' + (v % 10) as u8;
v /= 10;
}
// SAFETY: Per the precondition.
unsafe {
write_bytes(self.buf, &s[..len])?;
}
}
// SAFETY: Per the precondition.
numfmt::Part::Copy(buf) => unsafe {
write_bytes(self.buf, buf)?;
},
}
}
Ok(())
}
/// Writes some data to the underlying buffer contained within this
/// formatter.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// formatter.write_str("Foo")
/// // This is equivalent to:
/// // write!(formatter, "Foo")
/// }
/// }
///
/// assert_eq!(format!("{Foo}"), "Foo");
/// assert_eq!(format!("{Foo:0>8}"), "Foo");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn write_str(&mut self, data: &str) -> Result {
self.buf.write_str(data)
}
/// Glue for usage of the [`write!`] macro with implementors of this trait.
///
/// This method should generally not be invoked manually, but rather through
/// the [`write!`] macro itself.
///
/// Writes some formatted information into this instance.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// formatter.write_fmt(format_args!("Foo {}", self.0))
/// }
/// }
///
/// assert_eq!(format!("{}", Foo(-1)), "Foo -1");
/// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
if let Some(s) = fmt.as_statically_known_str() {
self.buf.write_str(s)
} else {
write(self.buf, fmt)
}
}
/// Returns flags for formatting.
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[deprecated(
since = "1.24.0",
note = "use the `sign_plus`, `sign_minus`, `alternate`, \
or `sign_aware_zero_pad` methods instead"
)]
pub fn flags(&self) -> u32 {
// Extract the debug upper/lower hex, zero pad, alternate, and plus/minus flags
// to stay compatible with older versions of Rust.
self.options.flags >> 21 & 0x3F
}
/// Returns the character used as 'fill' whenever there is alignment.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let c = formatter.fill();
/// if let Some(width) = formatter.width() {
/// for _ in 0..width {
/// write!(formatter, "{c}")?;
/// }
/// Ok(())
/// } else {
/// write!(formatter, "{c}")
/// }
/// }
/// }
///
/// // We set alignment to the right with ">".
/// assert_eq!(format!("{Foo:G>3}"), "GGG");
/// assert_eq!(format!("{Foo:t>6}"), "tttttt");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn fill(&self) -> char {
self.options.get_fill()
}
/// Returns a flag indicating what form of alignment was requested.
///
/// # Examples
///
/// ```
/// use std::fmt::{self, Alignment};
///
/// struct Foo;
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// let s = if let Some(s) = formatter.align() {
/// match s {
/// Alignment::Left => "left",
/// Alignment::Right => "right",
/// Alignment::Center => "center",
/// }
/// } else {
/// "into the void"
/// };
/// write!(formatter, "{s}")
/// }
/// }
///
/// assert_eq!(format!("{Foo:<}"), "left");
/// assert_eq!(format!("{Foo:>}"), "right");
/// assert_eq!(format!("{Foo:^}"), "center");
/// assert_eq!(format!("{Foo}"), "into the void");
/// ```
#[must_use]
#[stable(feature = "fmt_flags_align", since = "1.28.0")]
pub fn align(&self) -> Option<Alignment> {
self.options.get_align()
}
/// Returns the optionally specified integer width that the output should be.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// if let Some(width) = formatter.width() {
/// // If we received a width, we use it
/// write!(formatter, "{:width$}", format!("Foo({})", self.0), width = width)
/// } else {
/// // Otherwise we do nothing special
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(format!("{:10}", Foo(23)), "Foo(23) ");
/// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn width(&self) -> Option<usize> {
if self.options.flags & flags::WIDTH_FLAG == 0 {
None
} else {
Some(self.options.width as usize)
}
}
/// Returns the optionally specified precision for numeric types.
/// Alternatively, the maximum width for string types.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(f32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// if let Some(precision) = formatter.precision() {
/// // If we received a precision, we use it.
/// write!(formatter, "Foo({1:.*})", precision, self.0)
/// } else {
/// // Otherwise we default to 2.
/// write!(formatter, "Foo({:.2})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
/// assert_eq!(format!("{}", Foo(23.2)), "Foo(23.20)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn precision(&self) -> Option<usize> {
if self.options.flags & flags::PRECISION_FLAG == 0 {
None
} else {
Some(self.options.precision as usize)
}
}
/// Determines if the `+` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// if formatter.sign_plus() {
/// write!(formatter,
/// "Foo({}{})",
/// if self.0 < 0 { '-' } else { '+' },
/// self.0.abs())
/// } else {
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(format!("{:+}", Foo(23)), "Foo(+23)");
/// assert_eq!(format!("{:+}", Foo(-23)), "Foo(-23)");
/// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_plus(&self) -> bool {
self.options.flags & flags::SIGN_PLUS_FLAG != 0
}
/// Determines if the `-` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// if formatter.sign_minus() {
/// // You want a minus sign? Have one!
/// write!(formatter, "-Foo({})", self.0)
/// } else {
/// write!(formatter, "Foo({})", self.0)
/// }
/// }
/// }
///
/// assert_eq!(format!("{:-}", Foo(23)), "-Foo(23)");
/// assert_eq!(format!("{}", Foo(23)), "Foo(23)");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_minus(&self) -> bool {
self.options.flags & flags::SIGN_MINUS_FLAG != 0
}
/// Determines if the `#` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// if formatter.alternate() {
/// write!(formatter, "Foo({})", self.0)
/// } else {
/// write!(formatter, "{}", self.0)
/// }
/// }
/// }
///
/// assert_eq!(format!("{:#}", Foo(23)), "Foo(23)");
/// assert_eq!(format!("{}", Foo(23)), "23");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn alternate(&self) -> bool {
self.options.flags & flags::ALTERNATE_FLAG != 0
}
/// Determines if the `0` flag was specified.
///
/// # Examples
///
/// ```
/// use std::fmt;
///
/// struct Foo(i32);
///
/// impl fmt::Display for Foo {
/// fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
/// assert!(formatter.sign_aware_zero_pad());
/// assert_eq!(formatter.width(), Some(4));
/// // We ignore the formatter's options.
/// write!(formatter, "{}", self.0)
/// }
/// }
///
/// assert_eq!(format!("{:04}", Foo(23)), "23");
/// ```
#[must_use]
#[stable(feature = "fmt_flags", since = "1.5.0")]
pub fn sign_aware_zero_pad(&self) -> bool {
self.options.flags & flags::SIGN_AWARE_ZERO_PAD_FLAG != 0
}
// FIXME: Decide what public API we want for these two flags.
// https://github.com/rust-lang/rust/issues/48584
fn debug_lower_hex(&self) -> bool {
self.options.flags & flags::DEBUG_LOWER_HEX_FLAG != 0
}
fn debug_upper_hex(&self) -> bool {
self.options.flags & flags::DEBUG_UPPER_HEX_FLAG != 0
}
/// Creates a [`DebugStruct`] builder designed to assist with creation of
/// [`fmt::Debug`] implementations for structs.
///
/// [`fmt::Debug`]: self::Debug
///
/// # Examples
///
/// ```rust
/// use std::fmt;
/// use std::net::Ipv4Addr;
///
/// struct Foo {
/// bar: i32,
/// baz: String,
/// addr: Ipv4Addr,
/// }
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_struct("Foo")
/// .field("bar", &self.bar)
/// .field("baz", &self.baz)
/// .field("addr", &format_args!("{}", self.addr))
/// .finish()
/// }
/// }
///
/// assert_eq!(
/// "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
/// format!("{:?}", Foo {
/// bar: 10,
/// baz: "Hello World".to_string(),
/// addr: Ipv4Addr::new(127, 0, 0, 1),
/// })
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
builders::debug_struct_new(self, name)
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_struct_fields_finish` is more general, but this is
/// faster for 1 field.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field1_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_struct_fields_finish` is more general, but this is
/// faster for 2 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field2_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_struct_fields_finish` is more general, but this is
/// faster for 3 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field3_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_struct_fields_finish` is more general, but this is
/// faster for 4 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field4_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
name4: &str,
value4: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.field(name4, value4);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_struct_fields_finish` is more general, but this is
/// faster for 5 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_field5_finish<'b>(
&'b mut self,
name: &str,
name1: &str,
value1: &dyn Debug,
name2: &str,
value2: &dyn Debug,
name3: &str,
value3: &dyn Debug,
name4: &str,
value4: &dyn Debug,
name5: &str,
value5: &dyn Debug,
) -> Result {
let mut builder = builders::debug_struct_new(self, name);
builder.field(name1, value1);
builder.field(name2, value2);
builder.field(name3, value3);
builder.field(name4, value4);
builder.field(name5, value5);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller binaries.
/// For the cases not covered by `debug_struct_field[12345]_finish`.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_struct_fields_finish<'b>(
&'b mut self,
name: &str,
names: &[&str],
values: &[&dyn Debug],
) -> Result {
assert_eq!(names.len(), values.len());
let mut builder = builders::debug_struct_new(self, name);
for (name, value) in iter::zip(names, values) {
builder.field(name, value);
}
builder.finish()
}
/// Creates a `DebugTuple` builder designed to assist with creation of
/// `fmt::Debug` implementations for tuple structs.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
/// use std::marker::PhantomData;
///
/// struct Foo<T>(i32, String, PhantomData<T>);
///
/// impl<T> fmt::Debug for Foo<T> {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_tuple("Foo")
/// .field(&self.0)
/// .field(&self.1)
/// .field(&format_args!("_"))
/// .finish()
/// }
/// }
///
/// assert_eq!(
/// "Foo(10, \"Hello\", _)",
/// format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
builders::debug_tuple_new(self, name)
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_tuple_fields_finish` is more general, but this is faster
/// for 1 field.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field1_finish<'b>(&'b mut self, name: &str, value1: &dyn Debug) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_tuple_fields_finish` is more general, but this is faster
/// for 2 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field2_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_tuple_fields_finish` is more general, but this is faster
/// for 3 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field3_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_tuple_fields_finish` is more general, but this is faster
/// for 4 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field4_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
value4: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.field(value4);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. `debug_tuple_fields_finish` is more general, but this is faster
/// for 5 fields.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_field5_finish<'b>(
&'b mut self,
name: &str,
value1: &dyn Debug,
value2: &dyn Debug,
value3: &dyn Debug,
value4: &dyn Debug,
value5: &dyn Debug,
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
builder.field(value1);
builder.field(value2);
builder.field(value3);
builder.field(value4);
builder.field(value5);
builder.finish()
}
/// Shrinks `derive(Debug)` code, for faster compilation and smaller
/// binaries. For the cases not covered by `debug_tuple_field[12345]_finish`.
#[doc(hidden)]
#[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
pub fn debug_tuple_fields_finish<'b>(
&'b mut self,
name: &str,
values: &[&dyn Debug],
) -> Result {
let mut builder = builders::debug_tuple_new(self, name);
for value in values {
builder.field(value);
}
builder.finish()
}
/// Creates a `DebugList` builder designed to assist with creation of
/// `fmt::Debug` implementations for list-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<i32>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_list().entries(self.0.iter()).finish()
/// }
/// }
///
/// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
builders::debug_list_new(self)
}
/// Creates a `DebugSet` builder designed to assist with creation of
/// `fmt::Debug` implementations for set-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<i32>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_set().entries(self.0.iter()).finish()
/// }
/// }
///
/// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");
/// ```
///
/// [`format_args!`]: crate::format_args
///
/// In this more complex example, we use [`format_args!`] and `.debug_set()`
/// to build a list of match arms:
///
/// ```rust
/// use std::fmt;
///
/// struct Arm<'a, L, R>(&'a (L, R));
/// struct Table<'a, K, V>(&'a [(K, V)], V);
///
/// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
/// where
/// L: 'a + fmt::Debug, R: 'a + fmt::Debug
/// {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// L::fmt(&(self.0).0, fmt)?;
/// fmt.write_str(" => ")?;
/// R::fmt(&(self.0).1, fmt)
/// }
/// }
///
/// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
/// where
/// K: 'a + fmt::Debug, V: 'a + fmt::Debug
/// {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_set()
/// .entries(self.0.iter().map(Arm))
/// .entry(&Arm(&(format_args!("_"), &self.1)))
/// .finish()
/// }
/// }
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
builders::debug_set_new(self)
}
/// Creates a `DebugMap` builder designed to assist with creation of
/// `fmt::Debug` implementations for map-like structures.
///
/// # Examples
///
/// ```rust
/// use std::fmt;
///
/// struct Foo(Vec<(String, i32)>);
///
/// impl fmt::Debug for Foo {
/// fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
/// fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
/// }
/// }
///
/// assert_eq!(
/// format!("{:?}", Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
/// r#"{"A": 10, "B": 11}"#
/// );
/// ```
#[stable(feature = "debug_builders", since = "1.2.0")]
pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
builders::debug_map_new(self)
}
/// Returns the sign of this formatter (`+` or `-`).
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn sign(&self) -> Option<Sign> {
self.options.get_sign()
}
/// Returns the formatting options this formatter corresponds to.
#[unstable(feature = "formatting_options", issue = "118117")]
pub const fn options(&self) -> FormattingOptions {
self.options
}
}
#[stable(since = "1.2.0", feature = "formatter_write")]
impl Write for Formatter<'_> {
fn write_str(&mut self, s: &str) -> Result {
self.buf.write_str(s)
}
fn write_char(&mut self, c: char) -> Result {
self.buf.write_char(c)
}
#[inline]
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
if let Some(s) = args.as_statically_known_str() {
self.buf.write_str(s)
} else {
write(self.buf, args)
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for Error {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt("an error occurred when formatting an argument", f)
}
}
// Implementations of the core formatting traits
macro_rules! fmt_refs {
($($tr:ident),*) => {
$(
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + $tr> $tr for &T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + $tr> $tr for &mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
}
)*
}
}
fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
#[unstable(feature = "never_type", issue = "35121")]
impl Debug for ! {
#[inline]
fn fmt(&self, _: &mut Formatter<'_>) -> Result {
*self
}
}
#[unstable(feature = "never_type", issue = "35121")]
impl Display for ! {
#[inline]
fn fmt(&self, _: &mut Formatter<'_>) -> Result {
*self
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for bool {
#[inline]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt(self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for bool {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Display::fmt(if *self { "true" } else { "false" }, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for str {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.write_char('"')?;
// substring we know is printable
let mut printable_range = 0..0;
fn needs_escape(b: u8) -> bool {
b > 0x7E || b < 0x20 || b == b'\\' || b == b'"'
}
// the loop here first skips over runs of printable ASCII as a fast path.
// other chars (unicode, or ASCII that needs escaping) are then handled per-`char`.
let mut rest = self;
while rest.len() > 0 {
let Some(non_printable_start) = rest.as_bytes().iter().position(|&b| needs_escape(b))
else {
printable_range.end += rest.len();
break;
};
printable_range.end += non_printable_start;
// SAFETY: the position was derived from an iterator, so is known to be within bounds, and at a char boundary
rest = unsafe { rest.get_unchecked(non_printable_start..) };
let mut chars = rest.chars();
if let Some(c) = chars.next() {
let esc = c.escape_debug_ext(EscapeDebugExtArgs {
escape_grapheme_extended: true,
escape_single_quote: false,
escape_double_quote: true,
});
if esc.len() != 1 {
f.write_str(&self[printable_range.clone()])?;
Display::fmt(&esc, f)?;
printable_range.start = printable_range.end + c.len_utf8();
}
printable_range.end += c.len_utf8();
}
rest = chars.as_str();
}
f.write_str(&self[printable_range])?;
f.write_char('"')
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for str {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.pad(self)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for char {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.write_char('\'')?;
let esc = self.escape_debug_ext(EscapeDebugExtArgs {
escape_grapheme_extended: true,
escape_single_quote: true,
escape_double_quote: false,
});
Display::fmt(&esc, f)?;
f.write_char('\'')
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Display for char {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
if f.options.flags & (flags::WIDTH_FLAG | flags::PRECISION_FLAG) == 0 {
f.write_char(*self)
} else {
f.pad(self.encode_utf8(&mut [0; MAX_LEN_UTF8]))
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *const T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
if <<T as core::ptr::Pointee>::Metadata as core::unit::IsUnit>::is_unit() {
pointer_fmt_inner(self.expose_provenance(), f)
} else {
f.debug_struct("Pointer")
.field_with("addr", |f| pointer_fmt_inner(self.expose_provenance(), f))
.field("metadata", &core::ptr::metadata(*self))
.finish()
}
}
}
/// Since the formatting will be identical for all pointer types, uses a
/// non-monomorphized implementation for the actual formatting to reduce the
/// amount of codegen work needed.
///
/// This uses `ptr_addr: usize` and not `ptr: *const ()` to be able to use this for
/// `fn(...) -> ...` without using [problematic] "Oxford Casts".
///
/// [problematic]: https://github.com/rust-lang/rust/issues/95489
pub(crate) fn pointer_fmt_inner(ptr_addr: usize, f: &mut Formatter<'_>) -> Result {
let old_options = f.options;
// The alternate flag is already treated by LowerHex as being special-
// it denotes whether to prefix with 0x. We use it to work out whether
// or not to zero extend, and then unconditionally set it to get the
// prefix.
if f.options.get_alternate() {
f.options.sign_aware_zero_pad(true);
if f.options.get_width().is_none() {
f.options.width(Some((usize::BITS / 4) as u16 + 2));
}
}
f.options.alternate(true);
let ret = LowerHex::fmt(&ptr_addr, f);
f.options = old_options;
ret
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for *mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(*self as *const T), f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(*self as *const T), f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Pointer for &mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(&(&**self as *const T), f)
}
}
// Implementation of Display/Debug for various core types
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *const T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for *mut T {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Pointer::fmt(self, f)
}
}
macro_rules! peel {
($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
}
macro_rules! tuple {
() => ();
( $($name:ident,)+ ) => (
maybe_tuple_doc! {
$($name)+ @
#[stable(feature = "rust1", since = "1.0.0")]
impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
#[allow(non_snake_case, unused_assignments)]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
let mut builder = f.debug_tuple("");
let ($(ref $name,)+) = *self;
$(
builder.field(&$name);
)+
builder.finish()
}
}
}
peel! { $($name,)+ }
)
}
macro_rules! maybe_tuple_doc {
($a:ident @ #[$meta:meta] $item:item) => {
#[doc(fake_variadic)]
#[doc = "This trait is implemented for tuples up to twelve items long."]
#[$meta]
$item
};
($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
#[doc(hidden)]
#[$meta]
$item
};
}
macro_rules! last_type {
($a:ident,) => { $a };
($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
}
tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Debug> Debug for [T] {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_list().entries(self.iter()).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for () {
#[inline]
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.pad("()")
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Debug for PhantomData<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
write!(f, "PhantomData<{}>", crate::any::type_name::<T>())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Copy + Debug> Debug for Cell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("Cell").field("value", &self.get()).finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
let mut d = f.debug_struct("RefCell");
match self.try_borrow() {
Ok(borrow) => d.field("value", &borrow),
Err(_) => d.field("value", &format_args!("<borrowed>")),
};
d.finish()
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Debug::fmt(&**self, f)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
Debug::fmt(&*(self.deref()), f)
}
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T: ?Sized> Debug for UnsafeCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("UnsafeCell").finish_non_exhaustive()
}
}
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
impl<T: ?Sized> Debug for SyncUnsafeCell<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> Result {
f.debug_struct("SyncUnsafeCell").finish_non_exhaustive()
}
}
// If you expected tests to be here, look instead at coretests/tests/fmt/;
// it's a lot easier than creating all of the rt::Piece structures here.
// There are also tests in alloctests/tests/fmt.rs, for those that need allocations.