| //! Utilities for dynamic typing or type reflection. |
| //! |
| //! # `Any` and `TypeId` |
| //! |
| //! `Any` itself can be used to get a `TypeId`, and has more features when used |
| //! as a trait object. As `&dyn Any` (a borrowed trait object), it has the `is` |
| //! and `downcast_ref` methods, to test if the contained value is of a given type, |
| //! and to get a reference to the inner value as a type. As `&mut dyn Any`, there |
| //! is also the `downcast_mut` method, for getting a mutable reference to the |
| //! inner value. `Box<dyn Any>` adds the `downcast` method, which attempts to |
| //! convert to a `Box<T>`. See the [`Box`] documentation for the full details. |
| //! |
| //! Note that `&dyn Any` is limited to testing whether a value is of a specified |
| //! concrete type, and cannot be used to test whether a type implements a trait. |
| //! |
| //! [`Box`]: ../../std/boxed/struct.Box.html |
| //! |
| //! # Smart pointers and `dyn Any` |
| //! |
| //! One piece of behavior to keep in mind when using `Any` as a trait object, |
| //! especially with types like `Box<dyn Any>` or `Arc<dyn Any>`, is that simply |
| //! calling `.type_id()` on the value will produce the `TypeId` of the |
| //! *container*, not the underlying trait object. This can be avoided by |
| //! converting the smart pointer into a `&dyn Any` instead, which will return |
| //! the object's `TypeId`. For example: |
| //! |
| //! ``` |
| //! use std::any::{Any, TypeId}; |
| //! |
| //! let boxed: Box<dyn Any> = Box::new(3_i32); |
| //! |
| //! // You're more likely to want this: |
| //! let actual_id = (&*boxed).type_id(); |
| //! // ... than this: |
| //! let boxed_id = boxed.type_id(); |
| //! |
| //! assert_eq!(actual_id, TypeId::of::<i32>()); |
| //! assert_eq!(boxed_id, TypeId::of::<Box<dyn Any>>()); |
| //! ``` |
| //! |
| //! ## Examples |
| //! |
| //! Consider a situation where we want to log out a value passed to a function. |
| //! We know the value we're working on implements Debug, but we don't know its |
| //! concrete type. We want to give special treatment to certain types: in this |
| //! case printing out the length of String values prior to their value. |
| //! We don't know the concrete type of our value at compile time, so we need to |
| //! use runtime reflection instead. |
| //! |
| //! ```rust |
| //! use std::fmt::Debug; |
| //! use std::any::Any; |
| //! |
| //! // Logger function for any type that implements Debug. |
| //! fn log<T: Any + Debug>(value: &T) { |
| //! let value_any = value as &dyn Any; |
| //! |
| //! // Try to convert our value to a `String`. If successful, we want to |
| //! // output the `String`'s length as well as its value. If not, it's a |
| //! // different type: just print it out unadorned. |
| //! match value_any.downcast_ref::<String>() { |
| //! Some(as_string) => { |
| //! println!("String ({}): {}", as_string.len(), as_string); |
| //! } |
| //! None => { |
| //! println!("{value:?}"); |
| //! } |
| //! } |
| //! } |
| //! |
| //! // This function wants to log its parameter out prior to doing work with it. |
| //! fn do_work<T: Any + Debug>(value: &T) { |
| //! log(value); |
| //! // ...do some other work |
| //! } |
| //! |
| //! fn main() { |
| //! let my_string = "Hello World".to_string(); |
| //! do_work(&my_string); |
| //! |
| //! let my_i8: i8 = 100; |
| //! do_work(&my_i8); |
| //! } |
| //! ``` |
| //! |
| |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| use crate::fmt; |
| use crate::hash; |
| use crate::intrinsics; |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Any trait |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// A trait to emulate dynamic typing. |
| /// |
| /// Most types implement `Any`. However, any type which contains a non-`'static` reference does not. |
| /// See the [module-level documentation][mod] for more details. |
| /// |
| /// [mod]: crate::any |
| // This trait is not unsafe, though we rely on the specifics of it's sole impl's |
| // `type_id` function in unsafe code (e.g., `downcast`). Normally, that would be |
| // a problem, but because the only impl of `Any` is a blanket implementation, no |
| // other code can implement `Any`. |
| // |
| // We could plausibly make this trait unsafe -- it would not cause breakage, |
| // since we control all the implementations -- but we choose not to as that's |
| // both not really necessary and may confuse users about the distinction of |
| // unsafe traits and unsafe methods (i.e., `type_id` would still be safe to call, |
| // but we would likely want to indicate as such in documentation). |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[cfg_attr(not(test), rustc_diagnostic_item = "Any")] |
| pub trait Any: 'static { |
| /// Gets the `TypeId` of `self`. |
| /// |
| /// If called on a `dyn Any` trait object |
| /// (or a trait object of a subtrait of `Any`), |
| /// this returns the `TypeId` of the underlying |
| /// concrete type, not that of `dyn Any` itself. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::{Any, TypeId}; |
| /// |
| /// fn is_string(s: &dyn Any) -> bool { |
| /// TypeId::of::<String>() == s.type_id() |
| /// } |
| /// |
| /// assert_eq!(is_string(&0), false); |
| /// assert_eq!(is_string(&"cookie monster".to_string()), true); |
| /// ``` |
| #[stable(feature = "get_type_id", since = "1.34.0")] |
| fn type_id(&self) -> TypeId; |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<T: 'static + ?Sized> Any for T { |
| fn type_id(&self) -> TypeId { |
| TypeId::of::<T>() |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // Extension methods for Any trait objects. |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl fmt::Debug for dyn Any { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| // Ensure that the result of e.g., joining a thread can be printed and |
| // hence used with `unwrap`. May eventually no longer be needed if |
| // dispatch works with upcasting. |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl fmt::Debug for dyn Any + Send { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| impl fmt::Debug for dyn Any + Send + Sync { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Any").finish_non_exhaustive() |
| } |
| } |
| |
| impl dyn Any { |
| /// Returns `true` if the inner type is the same as `T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &dyn Any) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| // Get `TypeId` of the type this function is instantiated with. |
| let t = TypeId::of::<T>(); |
| |
| // Get `TypeId` of the type in the trait object (`self`). |
| let concrete = self.type_id(); |
| |
| // Compare both `TypeId`s on equality. |
| t == concrete |
| } |
| |
| /// Returns some reference to the inner value if it is of type `T`, or |
| /// `None` if it isn't. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &dyn Any) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| if self.is::<T>() { |
| // SAFETY: just checked whether we are pointing to the correct type, and we can rely on |
| // that check for memory safety because we have implemented Any for all types; no other |
| // impls can exist as they would conflict with our impl. |
| unsafe { Some(self.downcast_ref_unchecked()) } |
| } else { |
| None |
| } |
| } |
| |
| /// Returns some mutable reference to the inner value if it is of type `T`, or |
| /// `None` if it isn't. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut dyn Any) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| if self.is::<T>() { |
| // SAFETY: just checked whether we are pointing to the correct type, and we can rely on |
| // that check for memory safety because we have implemented Any for all types; no other |
| // impls can exist as they would conflict with our impl. |
| unsafe { Some(self.downcast_mut_unchecked()) } |
| } else { |
| None |
| } |
| } |
| |
| /// Returns a reference to the inner value as type `dyn T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// The contained value must be of type `T`. Calling this method |
| /// with the incorrect type is *undefined behavior*. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| debug_assert!(self.is::<T>()); |
| // SAFETY: caller guarantees that T is the correct type |
| unsafe { &*(self as *const dyn Any as *const T) } |
| } |
| |
| /// Returns a mutable reference to the inner value as type `dyn T`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// The contained value must be of type `T`. Calling this method |
| /// with the incorrect type is *undefined behavior*. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| debug_assert!(self.is::<T>()); |
| // SAFETY: caller guarantees that T is the correct type |
| unsafe { &mut *(self as *mut dyn Any as *mut T) } |
| } |
| } |
| |
| impl dyn Any + Send { |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &(dyn Any + Send)) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| <dyn Any>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &(dyn Any + Send)) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| <dyn Any>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut (dyn Any + Send)) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| <dyn Any>::downcast_mut::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// Same as the method on the type `dyn Any`. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) } |
| } |
| |
| /// Forwards to the method defined on the type `dyn Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| /// |
| /// # Safety |
| /// |
| /// Same as the method on the type `dyn Any`. |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_mut_unchecked::<T>(self) } |
| } |
| } |
| |
| impl dyn Any + Send + Sync { |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn is_string(s: &(dyn Any + Send + Sync)) { |
| /// if s.is::<String>() { |
| /// println!("It's a string!"); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// is_string(&0); |
| /// is_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn is<T: Any>(&self) -> bool { |
| <dyn Any>::is::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn print_if_string(s: &(dyn Any + Send + Sync)) { |
| /// if let Some(string) = s.downcast_ref::<String>() { |
| /// println!("It's a string({}): '{}'", string.len(), string); |
| /// } else { |
| /// println!("Not a string..."); |
| /// } |
| /// } |
| /// |
| /// print_if_string(&0); |
| /// print_if_string(&"cookie monster".to_string()); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn downcast_ref<T: Any>(&self) -> Option<&T> { |
| <dyn Any>::downcast_ref::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::Any; |
| /// |
| /// fn modify_if_u32(s: &mut (dyn Any + Send + Sync)) { |
| /// if let Some(num) = s.downcast_mut::<u32>() { |
| /// *num = 42; |
| /// } |
| /// } |
| /// |
| /// let mut x = 10u32; |
| /// let mut s = "starlord".to_string(); |
| /// |
| /// modify_if_u32(&mut x); |
| /// modify_if_u32(&mut s); |
| /// |
| /// assert_eq!(x, 42); |
| /// assert_eq!(&s, "starlord"); |
| /// ``` |
| #[stable(feature = "any_send_sync_methods", since = "1.28.0")] |
| #[inline] |
| pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> { |
| <dyn Any>::downcast_mut::<T>(self) |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// assert_eq!(*x.downcast_ref_unchecked::<usize>(), 1); |
| /// } |
| /// ``` |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_ref_unchecked::<T>(self) } |
| } |
| |
| /// Forwards to the method defined on the type `Any`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// #![feature(downcast_unchecked)] |
| /// |
| /// use std::any::Any; |
| /// |
| /// let mut x: Box<dyn Any> = Box::new(1_usize); |
| /// |
| /// unsafe { |
| /// *x.downcast_mut_unchecked::<usize>() += 1; |
| /// } |
| /// |
| /// assert_eq!(*x.downcast_ref::<usize>().unwrap(), 2); |
| /// ``` |
| #[unstable(feature = "downcast_unchecked", issue = "90850")] |
| #[inline] |
| pub unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T { |
| // SAFETY: guaranteed by caller |
| unsafe { <dyn Any>::downcast_mut_unchecked::<T>(self) } |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // TypeID and its methods |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /// A `TypeId` represents a globally unique identifier for a type. |
| /// |
| /// Each `TypeId` is an opaque object which does not allow inspection of what's |
| /// inside but does allow basic operations such as cloning, comparison, |
| /// printing, and showing. |
| /// |
| /// A `TypeId` is currently only available for types which ascribe to `'static`, |
| /// but this limitation may be removed in the future. |
| /// |
| /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth |
| /// noting that the hashes and ordering will vary between Rust releases. Beware |
| /// of relying on them inside of your code! |
| #[derive(Clone, Copy, Debug, Eq, PartialOrd, Ord)] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct TypeId { |
| t: u128, |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl PartialEq for TypeId { |
| #[inline] |
| fn eq(&self, other: &Self) -> bool { |
| self.t == other.t |
| } |
| } |
| |
| impl TypeId { |
| /// Returns the `TypeId` of the type this generic function has been |
| /// instantiated with. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::any::{Any, TypeId}; |
| /// |
| /// fn is_string<T: ?Sized + Any>(_s: &T) -> bool { |
| /// TypeId::of::<String>() == TypeId::of::<T>() |
| /// } |
| /// |
| /// assert_eq!(is_string(&0), false); |
| /// assert_eq!(is_string(&"cookie monster".to_string()), true); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "rust1", since = "1.0.0")] |
| #[rustc_const_unstable(feature = "const_type_id", issue = "77125")] |
| pub const fn of<T: ?Sized + 'static>() -> TypeId { |
| let t: u128 = intrinsics::type_id::<T>(); |
| TypeId { t } |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl hash::Hash for TypeId { |
| #[inline] |
| fn hash<H: hash::Hasher>(&self, state: &mut H) { |
| // We only hash the lower 64 bits of our (128 bit) internal numeric ID, |
| // because: |
| // - The hashing algorithm which backs `TypeId` is expected to be |
| // unbiased and high quality, meaning further mixing would be somewhat |
| // redundant compared to choosing (the lower) 64 bits arbitrarily. |
| // - `Hasher::finish` returns a u64 anyway, so the extra entropy we'd |
| // get from hashing the full value would probably not be useful |
| // (especially given the previous point about the lower 64 bits being |
| // high quality on their own). |
| // - It is correct to do so -- only hashing a subset of `self` is still |
| // with an `Eq` implementation that considers the entire value, as |
| // ours does. |
| (self.t as u64).hash(state); |
| } |
| } |
| |
| /// Returns the name of a type as a string slice. |
| /// |
| /// # Note |
| /// |
| /// This is intended for diagnostic use. The exact contents and format of the |
| /// string returned are not specified, other than being a best-effort |
| /// description of the type. For example, amongst the strings |
| /// that `type_name::<Option<String>>()` might return are `"Option<String>"` and |
| /// `"std::option::Option<std::string::String>"`. |
| /// |
| /// The returned string must not be considered to be a unique identifier of a |
| /// type as multiple types may map to the same type name. Similarly, there is no |
| /// guarantee that all parts of a type will appear in the returned string: for |
| /// example, lifetime specifiers are currently not included. In addition, the |
| /// output may change between versions of the compiler. |
| /// |
| /// The current implementation uses the same infrastructure as compiler |
| /// diagnostics and debuginfo, but this is not guaranteed. |
| /// |
| /// # Examples |
| /// |
| /// ```rust |
| /// assert_eq!( |
| /// std::any::type_name::<Option<String>>(), |
| /// "core::option::Option<alloc::string::String>", |
| /// ); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "type_name", since = "1.38.0")] |
| #[rustc_const_unstable(feature = "const_type_name", issue = "63084")] |
| pub const fn type_name<T: ?Sized>() -> &'static str { |
| intrinsics::type_name::<T>() |
| } |
| |
| /// Returns the type name of the pointed-to value as a string slice. |
| /// |
| /// This is the same as `type_name::<T>()`, but can be used where the type of a |
| /// variable is not easily available. |
| /// |
| /// # Note |
| /// |
| /// Like [`type_name`], this is intended for diagnostic use and the exact output is not |
| /// guaranteed. It provides a best-effort description, but the output may change between |
| /// versions of the compiler. |
| /// |
| /// In short: use this for debugging, avoid using the output to affect program behavior. More |
| /// information is available at [`type_name`]. |
| /// |
| /// Additionally, this function does not resolve trait objects. This means that |
| /// `type_name_of_val(&7u32 as &dyn Debug)` may return `"dyn Debug"`, but will not return `"u32"` |
| /// at this time. |
| /// |
| /// # Examples |
| /// |
| /// Prints the default integer and float types. |
| /// |
| /// ```rust |
| /// use std::any::type_name_of_val; |
| /// |
| /// let s = "foo"; |
| /// let x: i32 = 1; |
| /// let y: f32 = 1.0; |
| /// |
| /// assert!(type_name_of_val(&s).contains("str")); |
| /// assert!(type_name_of_val(&x).contains("i32")); |
| /// assert!(type_name_of_val(&y).contains("f32")); |
| /// ``` |
| #[must_use] |
| #[stable(feature = "type_name_of_val", since = "1.76.0")] |
| #[rustc_const_unstable(feature = "const_type_name", issue = "63084")] |
| pub const fn type_name_of_val<T: ?Sized>(_val: &T) -> &'static str { |
| type_name::<T>() |
| } |