Can C# Generic Constraints Specify Constructors with Specific Parameter Types?

C# generic constructor and parameter constraints

Generic constraints in C# allow specifying conditions on type parameters. The "new()" constraint is one of the common constraints that ensures that a type has a parameterless constructor. However, some situations may require more specific constraints on constructor parameters.

Question:

Can I specify a generic constraint that requires the existence of a constructor with a specific parameter type? For example, can a generic type T be constrained to have a constructor that accepts a "float[,]" parameter?

As shown below, directly trying to implement such constraints will cause compilation to fail:

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

Answer:

Unfortunately, such constraints cannot be specified directly in C#. However, there is a workaround available.

Workaround:

A common workaround is to provide a delegate that creates an object of the required type with specified parameters. This delegate can then be passed as a parameter to the generic method.

public class A {
    public static void Method<T>(T a, Func<float[,], T> creator) {
        // ... 执行某些操作 ...
    }
}

This approach allows flexibility in specifying constructor parameters, as the delegate can be customized to instantiate objects with specific values.

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