How do I use floating point number literals when using generic types?

Question

Regular float literals do not work:

extern crate num_traits;

use num_traits::float::Float;

fn scale_float(x: T) -> T {
    x * 0.54
}

f         


        

Answer 1

In certain cases, you can add a restriction that the generic type must be able to be multiplied by the type of the literal. Here, we allow any type that can be multiplied by a f64 so long as it produces the output type of T via the trait bound Mul:

use num_traits::float::Float; // 0.2.6
use std::ops::Mul;

fn scale_float(x: T) -> T
where
    T: Float + Mul,
{
    x * 0.54
}

fn main() {
    let a: f64 = scale_float(1.23);
}

This may not work directly for the original problem, but it might depending on what concrete types you need to work with.