77 lines
2.1 KiB
Rust
77 lines
2.1 KiB
Rust
#![feature(coerce_unsized, unsize)]
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use std::marker::Unsize;
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use std::ops::CoerceUnsized;
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fn identity_coercion(x: &(dyn Fn(u32) -> u32 + Send)) -> &dyn Fn(u32) -> u32 {
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x
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}
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fn fn_coercions(f: &fn(u32) -> u32) -> (unsafe fn(u32) -> u32, &(dyn Fn(u32) -> u32 + Send)) {
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(*f, f)
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}
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fn simple_array_coercion(x: &[u8; 3]) -> &[u8] {
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x
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}
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fn square(a: u32) -> u32 {
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a * a
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}
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#[derive(PartialEq, Eq)]
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struct PtrWrapper<'a, T: 'a + ?Sized>(u32, u32, (), &'a T);
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impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<PtrWrapper<'a, U>> for PtrWrapper<'a, T> {}
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struct TrivPtrWrapper<'a, T: 'a + ?Sized>(&'a T);
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impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<TrivPtrWrapper<'a, U>>
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for TrivPtrWrapper<'a, T>
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{
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}
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fn coerce_ptr_wrapper(p: PtrWrapper<[u8; 3]>) -> PtrWrapper<[u8]> {
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p
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}
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fn coerce_triv_ptr_wrapper(p: TrivPtrWrapper<[u8; 3]>) -> TrivPtrWrapper<[u8]> {
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p
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}
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fn coerce_fat_ptr_wrapper(
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p: PtrWrapper<dyn Fn(u32) -> u32 + Send>,
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) -> PtrWrapper<dyn Fn(u32) -> u32> {
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p
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}
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fn coerce_ptr_wrapper_poly<'a, T, Trait: ?Sized>(p: PtrWrapper<'a, T>) -> PtrWrapper<'a, Trait>
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where
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PtrWrapper<'a, T>: CoerceUnsized<PtrWrapper<'a, Trait>>,
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{
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p
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}
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fn main() {
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let a = [0, 1, 2];
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let square_local: fn(u32) -> u32 = square;
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let (f, g) = fn_coercions(&square_local);
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// cannot use `square as *const ()` because we can't know whether the compiler duplicates
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// functions, so two function pointers are only equal if they result from the same function
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// to function pointer cast
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assert_eq!(f as *const (), square_local as *const ());
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assert_eq!(g(4), 16);
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assert_eq!(identity_coercion(g)(5), 25);
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assert_eq!(simple_array_coercion(&a), &a);
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let w = coerce_ptr_wrapper(PtrWrapper(2, 3, (), &a));
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assert!(w == PtrWrapper(2, 3, (), &a) as PtrWrapper<[u8]>);
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let w = coerce_triv_ptr_wrapper(TrivPtrWrapper(&a));
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assert_eq!(&w.0, &a);
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let z = coerce_fat_ptr_wrapper(PtrWrapper(2, 3, (), &square_local));
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assert_eq!((z.3)(6), 36);
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let z: PtrWrapper<dyn Fn(u32) -> u32> =
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coerce_ptr_wrapper_poly(PtrWrapper(2, 3, (), &square_local));
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assert_eq!((z.3)(6), 36);
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}
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