String Find in Rust in Rust

In Rust, you can find the index of a substring using str::find():

s.find(sub)          // returns Some(index) of first occurrence, or None if not found
s.rfind(sub)         // returns Some(index) of last occurrence
s[start..].find(sub) // search starting from index `start`

Here are some examples:

let sentence = "Hello World";
let idx = sentence.find("World");
println!("{:?}", idx);  // Some(6)

if sentence.find("xyz").is_none() {
    println!("not found");
}

The index returned is the position of the first character of the found substring. Returns None if not found.