Compare structs for Equality

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• 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.

examples/struct/compare-structs-for-equality/src/main.rs

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

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

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

    let c = Thing {
        name: "Foo1".to_string(),
        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