src/libcore/internal_macros.rs

// implements the unary operator "op &T"
// based on "op T" where T is expected to be `Copy`able
macro_rules! forward_ref_unop {
    (impl $imp:ident, $method:ident for $t:ty) => {
        forward_ref_unop!(impl $imp, $method for $t,
                #[stable(feature = "rust1", since = "1.0.0")]);
    };
    (impl $imp:ident, $method:ident for $t:ty, #[$attr:meta]) => {
        #[$attr]
        impl $imp for &$t {
            type Output = <$t as $imp>::Output;

            #[inline]
            fn $method(self) -> <$t as $imp>::Output {
                $imp::$method(*self)
            }
        }
    }
}

// implements binary operators "&T op U", "T op &U", "&T op &U"
// based on "T op U" where T and U are expected to be `Copy`able
macro_rules! forward_ref_binop {
    (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
        forward_ref_binop!(impl $imp, $method for $t, $u,
                #[stable(feature = "rust1", since = "1.0.0")]);
    };
    (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
        #[$attr]
        impl<'a> $imp<$u> for &'a $t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: $u) -> <$t as $imp<$u>>::Output {
                $imp::$method(*self, other)
            }
        }

        #[$attr]
        impl $imp<&$u> for $t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                $imp::$method(self, *other)
            }
        }

        #[$attr]
        impl $imp<&$u> for &$t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: &$u) -> <$t as $imp<$u>>::Output {
                $imp::$method(*self, *other)
            }
        }
    }
}

// implements "T op= &U", based on "T op= U"
// where U is expected to be `Copy`able
macro_rules! forward_ref_op_assign {
    (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
        forward_ref_op_assign!(impl $imp, $method for $t, $u,
                #[stable(feature = "op_assign_builtins_by_ref", since = "1.22.0")]);
    };
    (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
        #[$attr]
        impl $imp<&$u> for $t {
            #[inline]
            fn $method(&mut self, other: &$u) {
                $imp::$method(self, *other);
            }
        }
    }
}

/// Create a zero-size type similar to a closure type, but named.
#[unstable(feature = "std_internals", issue = "0")]
macro_rules! impl_fn_for_zst {
    ($(
        $( #[$attr: meta] )*
        struct $Name: ident impl$( <$( $lifetime : lifetime ),+> )? Fn =
            |$( $arg: ident: $ArgTy: ty ),*| -> $ReturnTy: ty
            $body: block;
    )+) => {
        $(
            $( #[$attr] )*
            struct $Name;

            impl $( <$( $lifetime ),+> )? Fn<($( $ArgTy, )*)> for $Name {
                #[inline]
                extern "rust-call" fn call(&self, ($( $arg, )*): ($( $ArgTy, )*)) -> $ReturnTy {
                    $body
                }
            }

            impl $( <$( $lifetime ),+> )? FnMut<($( $ArgTy, )*)> for $Name {
                #[inline]
                extern "rust-call" fn call_mut(
                    &mut self,
                    ($( $arg, )*): ($( $ArgTy, )*)
                ) -> $ReturnTy {
                    Fn::call(&*self, ($( $arg, )*))
                }
            }

            impl $( <$( $lifetime ),+> )? FnOnce<($( $ArgTy, )*)> for $Name {
                type Output = $ReturnTy;

                #[inline]
                extern "rust-call" fn call_once(self, ($( $arg, )*): ($( $ArgTy, )*)) -> $ReturnTy {
                    Fn::call(&self, ($( $arg, )*))
                }
            }
        )+
    }
}

/// A macro for defining `#[cfg]` if-else statements.
///
/// The macro provided by this crate, `cfg_if`, is similar to the `if/elif` C
/// preprocessor macro by allowing definition of a cascade of `#[cfg]` cases,
/// emitting the implementation which matches first.
///
/// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code
/// without having to rewrite each clause multiple times.
///
/// # Example
///
/// ```
/// #[macro_use]
/// extern crate cfg_if;
///
/// cfg_if! {
///     if #[cfg(unix)] {
///         fn foo() { /* unix specific functionality */ }
///     } else if #[cfg(target_pointer_width = "32")] {
///         fn foo() { /* non-unix, 32-bit functionality */ }
///     } else {
///         fn foo() { /* fallback implementation */ }
///     }
/// }
///
/// # fn main() {}
/// ```
macro_rules! cfg_if {
    // match if/else chains with a final `else`
    ($(
        if #[cfg($($meta:meta),*)] { $($it:item)* }
    ) else * else {
        $($it2:item)*
    }) => {
        cfg_if! {
            @__items
            () ;
            $( ( ($($meta),*) ($($it)*) ), )*
            ( () ($($it2)*) ),
        }
    };

    // match if/else chains lacking a final `else`
    (
        if #[cfg($($i_met:meta),*)] { $($i_it:item)* }
        $(
            else if #[cfg($($e_met:meta),*)] { $($e_it:item)* }
        )*
    ) => {
        cfg_if! {
            @__items
            () ;
            ( ($($i_met),*) ($($i_it)*) ),
            $( ( ($($e_met),*) ($($e_it)*) ), )*
            ( () () ),
        }
    };

    // Internal and recursive macro to emit all the items
    //
    // Collects all the negated cfgs in a list at the beginning and after the
    // semicolon is all the remaining items
    (@__items ($($not:meta,)*) ; ) => {};
    (@__items ($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => {
        // Emit all items within one block, applying an approprate #[cfg]. The
        // #[cfg] will require all `$m` matchers specified and must also negate
        // all previous matchers.
        cfg_if! { @__apply cfg(all($($m,)* not(any($($not),*)))), $($it)* }

        // Recurse to emit all other items in `$rest`, and when we do so add all
        // our `$m` matchers to the list of `$not` matchers as future emissions
        // will have to negate everything we just matched as well.
        cfg_if! { @__items ($($not,)* $($m,)*) ; $($rest)* }
    };

    // Internal macro to Apply a cfg attribute to a list of items
    (@__apply $m:meta, $($it:item)*) => {
        $(#[$m] $it)*
    };
}