Is there a constraint that restricts my generic method to numeric types?

Question

Can anyone tell me if there is a way with generics to limit a generic type argument T to only:

• Int16
• Int32

Answer 1

Workaround using policies:

interface INumericPolicy
{
    T Zero();
    T Add(T a, T b);
    // add more functions here, such as multiplication etc.
}

struct NumericPolicies:
    INumericPolicy,
    INumericPolicy
    // add more INumericPolicy<> for different numeric types.
{
    int INumericPolicy.Zero() { return 0; }
    long INumericPolicy.Zero() { return 0; }
    int INumericPolicy.Add(int a, int b) { return a + b; }
    long INumericPolicy.Add(long a, long b) { return a + b; }
    // implement all functions from INumericPolicy<> interfaces.

    public static NumericPolicies Instance = new NumericPolicies();
}

Algorithms:

static class Algorithms
{
    public static T Sum(this P p, params T[] a)
        where P: INumericPolicy
    {
        var r = p.Zero();
        foreach(var i in a)
        {
            r = p.Add(r, i);
        }
        return r;
    }

}

Usage:

int i = NumericPolicies.Instance.Sum(1, 2, 3, 4, 5);
long l = NumericPolicies.Instance.Sum(1L, 2, 3, 4, 5);
NumericPolicies.Instance.Sum("www", "") // compile-time error.

The solution is compile-time safe. CityLizard Framework provides compiled version for .NET 4.0. The file is lib/NETFramework4.0/CityLizard.Policy.dll.

It's also available in Nuget: https://www.nuget.org/packages/CityLizard/. See CityLizard.Policy.I structure.