1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
|
use auto_impl::auto_impl;
/// This simple trait can be implemented for `Fn` types, but not for `FnMut` or
/// `FnOnce` types. The latter two types require a mutable reference to `self`
/// or a `self` by value to be called, but `greet()` only has an immutable
/// reference. Try creating an auto-impl for `FnMut`: you should get an error.
///
/// This attribute expands to the following impl (not exactly this code, but
/// equivalent, slightly uglier code):
///
/// ```
/// impl<F: Fn(&str)> Greeter for F {
/// fn greet(&self, name: &str) {
/// self(name)
/// }
/// }
/// ```
#[auto_impl(Fn)]
trait Greeter {
fn greet(&self, name: &str);
}
fn greet_people(greeter: impl Greeter) {
greeter.greet("Anna");
greeter.greet("Bob");
}
fn main() {
// We can simply pass a closure here, since this specific closure
// implements `Fn(&str)` and therefore also `Greeter`. Note that we need
// explicit type annotations here. This has nothing to do with `auto_impl`,
// but is simply a limitation of type inference.
greet_people(|name: &str| println!("Hallo {} :)", name));
}
|
