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ad03e4de18
4493: Provide builtin impls of Fn traits for fn-pointers r=flodiebold a=hban Meant to be, but isn't actually a fix for #2880. Consider this snippet: ```rust use std::marker::PhantomData; use std::ops::Deref; struct Lazy<T, F/* = fn() -> T*/>(F, PhantomData<T>); impl<T, F> Lazy<T, F> { pub fn new(f: F) -> Lazy<T, F> { Lazy(f, PhantomData) } } impl<T, F: FnOnce() -> T> Deref for Lazy<T, F> { type Target = T; fn deref(&self) -> &T { todo!() } } fn test() { let lazy1: Lazy<u32, _> = Lazy::new(|| 0u32); let r1 = lazy1.to_string(); fn make_u32_fn() -> u32 { todo!() } let make_u32_fn_ptr: fn() -> u32 = make_u32_fn; let lazy2: Lazy<u32, _> = Lazy::new(make_u32_fn_ptr); let r2 = lazy2.to_string(); } ``` * On current master: * When type default is commented-out, `r1` is correctly inferred, `r2` in _{unknown}_. * When type default is not commented-out, both `r1` and `r2` are _{unknown}_. * With this PR: * When type default is commented-out, both `r1` and `r2` are correctly inferred. * When type default is not commented-out, both `r1` and `r2` are _{unknown}_. Well, it's a improvement at least. I guess this thing with type defaults is a different problem. I also tried add Fn impls for fn items, but wasn't successful. So this PR only adds those impls for fn pointers. Co-authored-by: Hrvoje Ban <hban@users.noreply.github.com> |
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