Deref on a newtype in Rust

Deref lets a wrapper forward the inner type's methods without writing any.

use std::ops::Deref;

struct Handle(String);

impl Deref for Handle {
    type Target = String;

    fn deref(&self) -> &String {
        &self.0
    }
}

fn main() {
    let handle = Handle("ada_lovelace".to_string());
    println!("{}", handle.len());
    println!("{}", handle.to_uppercase());
    println!("{}", handle.starts_with("ada"));
    println!("{}", *handle);
}

How it works

1. deref returns a reference to the wrapped value.
2. Method calls then reach through the wrapper.
3. Use it for smart pointers and newtypes, not for inheritance.

Keywords and builtins used here

• Handle
• String
• Target
• deref
• fn
• for
• impl
• let
• main
• self
• struct
• type
• use

The run, in numbers

Lines

19

Characters to type

334

Tokens

111

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 63 seconds.

Type this snippet

Step 3 of 4 in Operators & access, step 14 of 19 in Traits & generics.

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