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 impl<'a, CapturedData: ?Sized, Function> ConstFnMutClosure<&'a mut CapturedData, Function> {
  27     /// Function for creating a new closure.
  28     ///
  29     /// `data` is the a mutable borrow of data that is captured from the environment.
  30     /// If you want Data to be a tuple of mutable Borrows, the struct must be constructed manually.
  31     ///
  32     /// `func` is the function of the closure, it gets the data and a tuple of the arguments closure
  33     ///   and return the return value of the closure.
  34     pub(crate) const fn new<ClosureArguments, ClosureReturnValue>(
  35         data: &'a mut CapturedData,
  36         func: Function,
  37     ) -> Self
  38     where
  39         Function: ~const Fn(&mut CapturedData, ClosureArguments) -> ClosureReturnValue,
  40     {
  41         Self { data, func }
  42     }
  43 }
  44
  45 macro_rules! impl_fn_mut_tuple {
  46     ($($var:ident)*) => {
  47         #[allow(unused_parens)]
  48         impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
  49             FnOnce<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  50         where
  51             Function: ~const Fn(($(&mut $var),*), ClosureArguments) -> ClosureReturnValue+ ~const Destruct,
  52         {
  53             type Output = ClosureReturnValue;
  54
  55             extern "rust-call" fn call_once(mut self, args: ClosureArguments) -> Self::Output {
  56             self.call_mut(args)
  57             }
  58         }
  59         #[allow(unused_parens)]
  60         impl<'a, $($var,)* ClosureArguments, Function, ClosureReturnValue> const
  61             FnMut<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  62         where
  63             Function: ~const Fn(($(&mut $var),*), ClosureArguments)-> ClosureReturnValue,
  64         {
  65             extern "rust-call" fn call_mut(&mut self, args: ClosureArguments) -> Self::Output {
  66                 #[allow(non_snake_case)]
  67                 let ($($var),*) = &mut self.data;
  68                 (self.func)(($($var),*), args)
  69             }
  70         }
  71     };
  72 }
  73 impl_fn_mut_tuple!(A);
  74 impl_fn_mut_tuple!(A B);
  75 impl_fn_mut_tuple!(A B C);
  76 impl_fn_mut_tuple!(A B C D);
  77 impl_fn_mut_tuple!(A B C D E);