Taking &str, returning String in Rust

The API convention: borrow the cheapest thing that works, own what you return.

fn shout(text: &str) -> String {
    text.to_uppercase()
}

fn initials(name: &str) -> String {
    name.split_whitespace()
        .filter_map(|part| part.chars().next())
        .collect()
}

fn main() {
    let owned = String::from("ada lovelace");
    println!("{}", shout("literal"));
    println!("{}", shout(&owned));
    println!("{}", shout(owned.as_str()));
    println!("{}", initials(&owned));
}

How it works

1. &str accepts both literals and String by deref.
2. Return String when the function creates new text.
3. as_str and & bridge the two directions.

Keywords and builtins used here

• String
• fn
• initials
• let
• main
• shout
• str

The run, in numbers

Lines

17

Characters to type

363

Tokens

128

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 81 seconds.

Type this snippet

Step 4 of 4 in Slices & strings, step 10 of 15 in Ownership & borrowing.

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