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Description
This code works:
fn main() {
let func: Box<Fn()> = Box::new(|| println!("called"));
func();
}As does placing it in an array:
fn main() {
let func: [Box<Fn()>; 1] = [Box::new(|| println!("called"))];
func[0]();
}However, using a Vec fails:
fn main() {
let func: Vec<Box<Fn()>> = vec![Box::new(|| println!("called"))];
func[0](); // error: expected function, found `Box<std::ops::Fn()>`
}Instead, it must be explicitly dereferenced:
fn main() {
let func: Vec<Box<Fn()>> = vec![Box::new(|| println!("called"))];
(*func[0])();
}It's even more annoying for Vec<Box<FnMut()>>:
fn main() {
let mut func: Vec<Box<FnMut()>> = vec![Box::new(|| println!("called"))];
// func[0](); // expected function, found `Box<std::ops::FnMut()>`
// (*func[0])(); // cannot borrow immutable `Box` content as mutable
(*&mut func[0])();
}Metadata
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Aatch commentedon Sep 29, 2016
The fact that this works for arrays, but not Vec suggests that it's probably related to associated types. It's possible that wherever the coercion from
&Box<Fn()>to&Fn()is done sees&<Vec<Box<Fn()>> as Index<usize>>::Outputinstead.Resolve the callee type in check_call before autoderef
Auto merge of #36822 - Aatch:resolve-callee-expr, r=luqmana
Resolve the callee type in check_call before autoderef
jonhoo commentedon Mar 7, 2017
This doesn't seem to be fully resolved:
shepmaster commentedon Nov 12, 2017
@jonhoo That may be #26186 instead.