library/core/src/const_closure.rs

   1 use crate::marker::Destruct;
   2 use crate::marker::Tuple;
   3
   4 /// Struct representing a closure with mutably borrowed data.
   5 ///
   6 /// Example:
   7 /// ```no_build
   8 /// #![feature(const_mut_refs)]
   9 /// use crate::const_closure::ConstFnMutClosure;
  10 /// const fn imp(state: &mut i32, (arg,): (i32,)) -> i32 {
  11 ///   *state += arg;
  12 ///   *state
  13 /// }
  14 /// let mut i = 5;
  15 /// let mut cl = ConstFnMutClosure::new(&mut i, imp);
  16 ///
  17 /// assert!(7 == cl(2));
  18 /// assert!(8 == cl(1));
  19 /// ```
  20 pub(crate) struct ConstFnMutClosure<CapturedData, Function> {
  21     /// The Data captured by the Closure.
  22     /// Must be either a (mutable) reference or a tuple of (mutable) references.
  23     pub data: CapturedData,
  24     /// The Function of the Closure, must be: Fn(CapturedData, ClosureArgs) -> ClosureReturn
  25     pub func: Function,
  26 }
  27 impl<'a, CapturedData: ?Sized, Function> ConstFnMutClosure<&'a mut CapturedData, Function> {
  28     /// Function for creating a new closure.
  29     ///
  30     /// `data` is the a mutable borrow of data that is captured from the environment.
  31     /// If you want Data to be a tuple of mutable Borrows, the struct must be constructed manually.
  32     ///
  33     /// `func` is the function of the closure, it gets the data and a tuple of the arguments closure
  34     ///   and return the return value of the closure.
  35     pub(crate) const fn new<ClosureArguments, ClosureReturnValue>(
  36         data: &'a mut CapturedData,
  37         func: Function,
  38     ) -> Self
  39     where
  40         Function: ~const Fn(&mut CapturedData, ClosureArguments) -> ClosureReturnValue,
  41     {
  42         Self { data, func }
  43     }
  44 }
  45
  46 macro_rules! impl_fn_mut_tuple {
  47     ($($var:ident)*) => {
  48         #[allow(unused_parens)]
  49         impl<'a, $($var,)* ClosureArguments: Tuple, Function, ClosureReturnValue> const
  50             FnOnce<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  51         where
  52             Function: ~const Fn(($(&mut $var),*), ClosureArguments) -> ClosureReturnValue+ ~const Destruct,
  53         {
  54             type Output = ClosureReturnValue;
  55
  56             extern "rust-call" fn call_once(mut self, args: ClosureArguments) -> Self::Output {
  57             self.call_mut(args)
  58             }
  59         }
  60         #[allow(unused_parens)]
  61         impl<'a, $($var,)* ClosureArguments: Tuple, Function, ClosureReturnValue> const
  62             FnMut<ClosureArguments> for ConstFnMutClosure<($(&'a mut $var),*), Function>
  63         where
  64             Function: ~const Fn(($(&mut $var),*), ClosureArguments)-> ClosureReturnValue,
  65         {
  66             extern "rust-call" fn call_mut(&mut self, args: ClosureArguments) -> Self::Output {
  67                 #[allow(non_snake_case)]
  68                 let ($($var),*) = &mut self.data;
  69                 (self.func)(($($var),*), args)
  70             }
  71         }
  72     };
  73 }
  74 impl_fn_mut_tuple!(A);
  75 impl_fn_mut_tuple!(A B);
  76 impl_fn_mut_tuple!(A B C);
  77 impl_fn_mut_tuple!(A B C D);
  78 impl_fn_mut_tuple!(A B C D E);