library/core/src/const_closure.rs

   1 use crate::marker::Destruct;
   2
   3 /// Struct representing a closure with mutably borrowed data.
   4 ///
   5 /// Example:
   6 /// ```no_build
   7 /// #![feature(const_mut_refs)]
   8 /// use crate::const_closure::ConstFnMutClosure;
   9 /// const fn imp(state: &mut i32, (arg,): (i32,)) -> i32 {
  10 ///   *state += arg;
  11 ///   *state
  12 /// }
  13 /// let mut i = 5;
  14 /// let mut cl = ConstFnMutClosure::new(&mut i, imp);
  15 ///
  16 /// assert!(7 == cl(2));
  17 /// assert!(8 == cl(1));
  18 /// ```
  19 pub(crate) struct ConstFnMutClosure<CapturedData, Function> {
  20     /// The Data captured by the Closure.
  21     /// Must be either a (mutable) reference or a tuple of (mutable) references.
  22     pub data: CapturedData,
  23     /// The Function of the Closure, must be: Fn(CapturedData, ClosureArgs) -> ClosureReturn
  24     pub func: Function,
  25 }
  26
  27 macro_rules! impl_fn_mut_tuple {
  28     ($($var:ident)*) => {
  29       #[allow(unused_parens)]
  30       impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
  31         FnOnce<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  32       where
  33         Function: ~const Fn(($(&mut $var),*), ClosureArguments) -> ClosureReturnValue+ ~const Destruct,
  34       {
  35         type Output = ClosureReturnValue;
  36
  37         extern "rust-call" fn call_once(mut self, args: ClosureArguments) -> Self::Output {
  38           self.call_mut(args)
  39         }
  40       }
  41       #[allow(unused_parens)]
  42       impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
  43         FnMut<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  44       where
  45         Function: ~const Fn(($(&mut $var),*), ClosureArguments)-> ClosureReturnValue,
  46       {
  47         extern "rust-call" fn call_mut(&mut self, args: ClosureArguments) -> Self::Output {
  48           #[allow(non_snake_case)]
  49           let ($($var),*) = &mut self.data;
  50           (self.func)(($($var),*), args)
  51         }
  52       }
  53
  54     };
  55   }
  56 impl_fn_mut_tuple!(A);
  57 impl_fn_mut_tuple!(A B);
  58 impl_fn_mut_tuple!(A B C);
  59 impl_fn_mut_tuple!(A B C D);
  60 impl_fn_mut_tuple!(A B C D E);