Derive Macro CommutativeMonoid 

#[derive(CommutativeMonoid)]

Derive macro for CommutativeMonoid.

Marker trait indicating that combine is commutative. Requires each field to implement CommutativeMonoid.

Example

#[derive(Semigroup, Monoid, CommutativeMonoid)]
struct Foo {
    a: i32,  // addition is commutative
    b: std::collections::HashSet<String>,  // union is commutative
}