Rust: core::ops::Fn(char) -> bool

Here’s a Rust error:

error: the trait `core::ops::Fn(char) -> bool` is not implemented for the type `&str`

I was trying to split a string of numbers with spaces a delimiter. Here’s the line for which this error occured:

let split: Vec<&str> = input_string.as_slice().split(" ").collect();

Apparently, split was expecting a single character, not a substring. This obtuse error was easily solved by changing the double-quotes to single-quotes.

let split: Vec<&str> = input_string.as_slice().split(' ').collect();