How Can I Constrain a Generic Type to Have a Specific Constructor in C#?

C# Generic Types: Constructor Parameter Constraints

C# allows generic methods to be constrained to types possessing parameterless constructors (where T : new()). However, directly specifying a constructor with particular parameter types as a constraint isn't supported.

Example of a valid constraint:

public class A
{
    public static T Method<T>(T a) where T : new()
    {
        // ... some code ...
        return new T();
    }
}

This correctly limits T to types with a default constructor. The following, however, will result in a compilation error:

public class A
{
    public static T Method<T>(T a) where T : new(float[,] u)
    {
        // ... some code ...
        return new T(new float[0, 0]);
    }
}

Alternative Approach

To work around this limitation, utilize a delegate to provide a constructor accepting the required parameter type:

public class A
{
    public static void Method<T>(T a, Func<float[,], T> creator)
    {
        // ... some code ...
        T instance = creator(new float[0, 0]); // Create T using the supplied delegate
    }
}

Here, the creator delegate receives a float[,] and returns a T instance. The Method function then employs this delegate for object creation. This offers flexibility in specifying constructor parameters without relying on direct constraint mechanisms.

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