What you are trying to do is call a closure from multiple threads. That is, share the closure across multiple threads. As soon as the phrase “share across multiple threads” crosses my mind, my first thought is to reach for Arc (at least until RFC 458 is implemented in some form, when & will become … Read more
This is a little surprising, but isn’t a bug. flat_map takes a FnMut as it needs to call the closure multiple times. The code with move on the inner closure fails because that closure is created multiple times, once for each inner_numbers. If I write the closures in explicit form (i.e. a struct that stores … Read more
As originally pointed out by DK., you can use a function to apply extra constraints to a closure’s arguments and return values: fn constrain<F>(f: F) -> F where F: for<‘a> Fn(&’a mut SplitWhitespace) -> Result<&’a str, ParserError>, { f } This gives you the full abilities of the where clause; in this case you can … Read more
Complementing the existing answer with some more code for demonstration purposes: Unboxed closure Use a generic type: struct Foo<F> where F: Fn(usize) -> usize, { pub foo: F, } impl<F> Foo<F> where F: Fn(usize) -> usize, { fn new(foo: F) -> Self { Self { foo } } } fn main() { let foo = … Read more
Chris Lattner wrote on the developer forums: This is a feature we intentionally do not want to support. There are a variety of things that will cause pointer equality of functions (in the swift type system sense, which includes several kinds of closures) to fail or change depending on optimization. If “===” were defined on … Read more