Compare structs for Equality

• Eq

• PartialEq

• Each data type in Rust either implements Eq or PartialEq to allow users to check if two objects of the same type are equal using either the == operator or the eq method.

• When creating a struct it does not automatically implement these traits, but we can add them.

• Primitive data types such as integers and strings implement both Eq and PartialEq.

• float on the other hand only implements PartialEq as a float can also be NaN that would break Eq.

• We can add the Eq trait to any struct and if all the elements of the struct implement Eq then we can add that too:

• It will automatically provide us with the possibility to use == or eq (or != or ne for that matter) on the values of that type.

• However Eq is mostly just an indication to the compiler, the actual implementation is in PartialEq so we need to add that too.

• In order for two objects of this type to be equal, all the fields have to be equal.

#[derive(PartialEq, Eq)]
struct Thing {
    name: String,
    number: i32,
}

fn main() {
    let a = Thing {
        name: String::from("Foo"),
        number: 42,
    };

    let b = Thing {
        name: String::from("Foo"),
        number: 42,
    };

    let c = Thing {
        name: String::from("Foo1"),
        number: 42,
    };

    println!("{}", a == b);
    println!("{}", a == c);

    // We cannot compare which is bigger as we have not implemented (or derived from) Ord or PartialOrd.
    // println!("{}", a < c);
}

true
false