Repository navigation
Calling and_then on Option<String> with a function that takes &str could provide a more helpful diagnostic #106342
Description
Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=d2e7d8643e1ae76544e6f0f1a117230b
fn produces_string() -> Option<String> {
Some("my cool string".to_owned())
}
fn takes_str(x: &str) -> Option<()> {
Some(())
}
fn main() {
let x = produces_string().and_then(takes_str);
}The current output is:
error[[E0631]](https://doc.rust-lang.org/stable/error-index.html#E0631): type mismatch in function arguments
--> src/main.rs:10:40
|
5 | fn takes_str(x: &str) -> Option<()> {
| ----------------------------------- found signature defined here
...
10 | let x = produces_string().and_then(takes_str);
| -------- ^^^^^^^^^ expected due to this
| |
| required by a bound introduced by this call
|
= note: expected function signature `fn(String) -> _`
found function signature `for<'a> fn(&'a str) -> _`
note: required by a bound in `Option::<T>::and_then`
The solution is to change:
-let x = produces_string().and_then(takes_str);
+let x = produces_string().as_deref().and_then(takes_str);It would be nice if rustc told me this.
Activity
y21 commentedon May 14, 2023
@rustbot claim
Rollup merge of rust-lang#111659 - y21:suggest-as-deref, r=cjgillot
Rollup merge of rust-lang#111659 - y21:suggest-as-deref, r=cjgillot