[jevgarrido]

Removing requirement Add from trait Zero.
Removing requirement Mul from trait One.

Broadens domain of applicability for traits Zero and One.
Semver-compatible modification

See #364

Visibility on consumer side

Zero does not imply Add anymore

This will now not compile

fn my_fun( input: T ) -> T
   where T: Zero
{
    input + T::zero()   
}

But this will

fn my_fun( input: T ) -> T
   where T: Zero + Add< T, Output = T >
{ //               ^^^^^^^^^^^^^^^^^^^^
    input + T::zero()   
}

So the Add and Mul operations become more explicit.

In practice this is not really noticeable because everyone just uses Float or Num if they want to add or multiply generically.

Can implement One without Mul (and Zero without Add)

This will now compile:

#[derive(Debug)]
struct MyStruct<T>(T);

use num_traits::One;

impl<T: One> One for MyStruct<T> {
    fn one() -> Self {
        Self( T::one() )
    }
}

// no need to implement Mul.

fn foo() {
    let recurse : MyStruct< MyStruct<f64> > = MyStruct( MyStruct::one() );

    println!( "{:?}", recurse );
}

This way we are able to use the Zero and One constructors right away, without worrying about the logic of adding or multiplying upfront.

---

Closes #364

[cuviper]

Semver-compatible modification

It is not, as already explained on the issue.

This will now not compile
[...]
In practice this is not really noticeable

No, we're not going to just hand-wave that away.