Traits for function items

[RalfJung]

Presumably this one:

Pre-RFC: FnStatic

Problem statement It is not possible to make function/closure combinators that return function pointers, even though it is possible to return a function pointer that wraps a trait associated function. Usecase The main usecase is efficiently allowing erganomic wrappers for callbacks in C ffi. For example, a wrapper around libc::signal that automatically wraps your signal handler so it saves and restores errno as required by the POSIX standard. The Trait #![feature(unboxed_closures)] #![feature…