compiler/rustc_error_codes/src/error_codes/E0631.md

   1 This error indicates a type mismatch in closure arguments.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0631
   6 fn foo<F: Fn(i32)>(f: F) {
   7 }
   8
   9 fn main() {
  10     foo(|x: &str| {});
  11 }
  12 ```
  13
  14 The error occurs because `foo` accepts a closure that takes an `i32` argument,
  15 but in `main`, it is passed a closure with a `&str` argument.
  16
  17 This can be resolved by changing the type annotation or removing it entirely
  18 if it can be inferred.
  19
  20 ```
  21 fn foo<F: Fn(i32)>(f: F) {
  22 }
  23
  24 fn main() {
  25     foo(|x: i32| {});
  26 }
  27 ```