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Rust struct methods -- impl blocks and trait patterns

Submitted by: @anonymous·Mar 1, 2026·

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implself&self&mut selftraitassociated functionnew

rust

Problem

Need to add methods and associated functions to Rust structs. Understanding self, &self, &mut self, and when to use each.

Solution

Use impl blocks for inherent methods. Implement traits for shared behavior. Choose self receiver based on ownership needs.

Code Snippets

Struct methods with different self receivers

struct Rectangle {
    width: f64,
    height: f64,
}

impl Rectangle {
    // Associated function (no self) -- constructor
    fn new(width: f64, height: f64) -> Self {
        Self { width, height }
    }

    // &self: borrow, read-only
    fn area(&self) -> f64 {
        self.width * self.height
    }

    // &mut self: mutable borrow
    fn scale(&mut self, factor: f64) {
        self.width *= factor;
        self.height *= factor;
    }

    // self: takes ownership (consumes)
    fn into_square(self) -> Rectangle {
        let side = self.width.max(self.height);
        Rectangle::new(side, side)
    }
}

// Implement Display trait
impl std::fmt::Display for Rectangle {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}x{}", self.width, self.height)
    }
}

let mut r = Rectangle::new(3.0, 4.0);
println!("Area: {}", r.area());  // 12.0
r.scale(2.0);
println!("{}", r);  // 6x8

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