Can I use '<' and '>' in match?

rust match quadratic
dawid picture dawid · Dec 17, 2017 · Viewed 8.2k times · Source

I am trying to do a simple quadratic function that would return number of roots and their values via an enum:

enum QuadraticResult {
    None,
    OneRoot(f32),
    TwoRoots(f32, f32),
}

fn solveQuadratic(a: f32, b: f32, c: f32) -> QuadraticResult {
    let delta = b * b - 4.0 * a * c;
    match delta {
        < 0 => return QuadraticResult::None,
        > 0 => return QuadraticResult::TwoRoots(0.0, 1.0),
        _ => return QuadraticResult::OneRoot(0.0),
    }
}

This doesn't compile as it complains about '<' and '>'. Is there a way to achieve this with match or do I need to use if

Answer

Jacob Krall picture Jacob Krall · Dec 17, 2017

You can use a match guard, but that feels more verbose than a plain if statement:

return match delta {
    d if d < 0 => QuadraticResult::None,
    d if d > 0 => QuadraticResult::TwoRoots(0.0, 1.0),
    _   => QuadraticResult::OneRoot(0.0),
}

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