PartialEq and Eq

Partial equality & Total equality.

Derivable: ✅

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

#[derive(PartialEq, Eq)]
pub struct User { name: String, favorite_number: i32 }

fn main() {
    let alice = User { name: "alice".to_string(), favorite_number: 1_000_042 };
    let bob = User { name: "bob".to_string(), favorite_number: 42 };

    dbg!(alice == alice);
    dbg!(alice == bob);
}

  • Equality-related methods. If a type implements PartialEq then you can use the ==/!= operator with that type.

  • A type can’t implement Eq without implementing PartialEq.

  • Reminder: Partial means “there are invalid members of this set for this function.”

    This doesn’t mean that equality will panic, or that it returns a result, just that there may be values that may not behave as you expect equality to behave.

    For example, with floating point values NaN is an outlier: NaN == NaN is false, despite bitwise equality.

    PartialEq exists to separate types like f32/f64 from types with Total Equality.

  • You can implement PartialEq between different types, but this is mostly useful for reference/smart pointer types.