Implementing multiparameter C++ template like behaviour on C# using Policy Pattern

Question

I\'m trying to implement a c++ like template with C# generics and policy pattern based on this answer

This is a sample of the pattern:

interface ISom         


        

Answer 1

Usually, policies should not contain data. For example,

interface ISomePolicy
{
    void _doSomething(T t, U u);
}

struct SomePolicyImplementation :
    ISomePolicy,
    ISomePolicy,
    ISomePolicy
{
    void ISomePolicy._doSomething(int t, int u)
        => Console.WriteLine("this is int, int");

    void ISomePolicy._doSomething(int t, double u)
        => Console.WriteLine("this is int, double");

    void ISomePolicy._doSomething(double t, double u)
        => Console.WriteLine("this is double, double");
}

static class SomePolicyExtension
{
    public static void doSomething(this P policy, T t, U u)
        where P : struct, ISomePolicy
        => policy._doSomething(t, u);
}

If you would like to combine policies and data then you may consider different interface

interface IEmbeddedPolicy
{
    void _doSomething(U u);
}

class MyClass :
    IEmbeddedPolicy,
    IEmbeddedPolicy
{
    public T Value { get; }

    public MyClass(T value) { this.Value = value; }

    void IEmbeddedPolicy._doSomething(int u)
        => Console.WriteLine("this is T, int");

    void IEmbeddedPolicy._doSomething(double u)
        => Console.WriteLine("this is T, double");
}

static class EmbeddedPolicyExtension
{
    public static void doSomething(this E embedded, U u)
        where E : IEmbeddedPolicy
        => embedded._doSomething(u);
}

Or combination of these two concepts

class MySuperClass:
    IEmbeddedPolicy,
    IEmbeddedPolicy
    where P: struct, ISomePolicy, ISomePolicy
{
    public T Value { get; }

    public MySuperClass(T value) { this.Value = value; }

    void IEmbeddedPolicy._doSomething(int u)
        => new P()._doSomething(this.Value, u);

    void IEmbeddedPolicy._doSomething(double u)
        => new P()._doSomething(this.Value, u);
}

Usage:

// independent policy
var policy = new SomePolicyImplementation();

policy.doSomething(5, 6);
policy.doSomething(5, 6.7);
policy.doSomething(5.3, 6.7);

// embedded policy
var my = new MyClass(54);
my.doSomething(5);
my.doSomething(89.7);

// combination
var x = new MySuperClass(53);
x.doSomething(9);
x.doSomething(18.3);