[Tip] Generic function compare any Integer or Float type with 0

[davyzhu]

Previously, I asked a question, got a solution, and I search on web, find 2 good approaches.

1. compare with T::default()
2. compare with 2 multiply itself (@steffahn mentioned INFINITY will lead to same result)
3. compare with itself sub itself (@jhpratt suggested)

use std::cmp::*;
use std::default::Default;
use std::ops::*;

fn is_zero_default<T>(a: T) -> bool
where
    T: PartialEq + Default,
{
    a == T::default()
}

fn is_zero_sub<T>(a: T) -> bool
where
    T: PartialEq + Copy + Sub<Output = T>,
{
    a == a - a
}

fn is_zero_add<T>(a: T) -> bool
where
    T: PartialEq + Copy + Add<Output = T>,
{
    a == (a + a)
}

fn main() {
    println!("{}", is_zero_default(0));
    println!("{}", is_zero_default(0.0));
    println!("{}", is_zero_add(0));
    println!("{}", is_zero_add(0.0));
    println!("{}", is_zero_sub(0));
    println!("{}", is_zero_sub(0.0));
}

[jhpratt]

The way I've done this in the past was to do a - a, which would generate zero from whatever value I passed. That way it's not needed to be passed explicitly.

[steffahn]

a == a + a will also be true for positive and negative infinity for floats.