Object destructuring is a syntax that allows you to unpack values from an object. Many modern languages have support for it. So let's have a look at an example:

struct User {
    name: String,
    age: u8
}

// Bad: This how I would naively write this
impl ToString for User {
    fn to_string(&self) -> String {
        format!("{name} ({age})", name=self.name, age=self.age)
    }
}

// Good: Take advantage of destructuring
impl ToString for User {
    fn to_string(&self) -> String {
        let User { name, age } = self;
        format!("{name} ({age})", name=name, age=age)
    }
}

Why does it matter? Well, let's have a look what happens when we add a field:

struct User {
    name: String,
    age: u8,
    height: u16 // in cm
}

The bad example will compile perfectly fine. Meanwhile when using destructuring we get:

error[E0027]: pattern does not mention field `height`
 --> src/lib.rs:9:13
  |
9 |         let User { name, age } = self;
  |             ^^^^^^^^^^^^^^^^^^ missing field `height`
  |
help: include the missing field in the pattern
  |
9 |         let User { name, age, height } = self;
  |                             ^^^^^^^^^^
help: if you don't care about this missing field, you can explicitly ignore it
  |
9 |         let User { name, age, .. } = self;
  |                             ^^^^^^

Thanks to object destructuring we remember to update our code:

impl ToString for User {
    fn to_string(&self) -> String {
        let User { name, age, height } = self;
        format!("{name} ({age}, {height} cm)", name=name, age=age, height=height)
    }
}

Published on 2021-08-28.