The trait `FnMut<(char,)>` is not implemented for `String` when trying to split a string

Question

I need to split a String (not &str) by another String:

use std::str::Split;

fn main() {
    let x = "".to_string().split("".to_string());
}

Why do I get this error and how to avoid it if I already have to operate on strings?

error[E0277]: the trait bound `std::string::String: std::ops::FnMut<(char,)>` is not satisfied
 --> src/main.rs:4:32
  |
4 |         let x = "".to_string().split("".to_string());
  |                                ^^^^^ the trait `std::ops::FnMut<(char,)>` is not implemented for `std::string::String`
  |
  = note: required because of the requirements on the impl of `std::str::pattern::Pattern<'_>` for `std::string::String`

According to the #rust-beginners IRC channel, this might be an example of Deref failing in 1.20.0-nightly. How to split a string in Rust? doesn't address the problem of splitting by String, not &str.

Answer 1

All is in the documentation. You can provide one of:

• A &str,
• A char,
• A closure,

Those three types implement the Pattern trait. You are giving a String to split instead of a &str.

Example:

fn main() {
    let x = "".to_string();
    let split = x.split("");
}