Can C# Generic Constructors Enforce Specific Parameter Types Beyond Parameterless Constructors?

Can C# generic constructor force the parameter type to be specified? Beyond the limitations of parameterless constructors

In C#, constraints can be placed on generic methods to ensure that specific requirements are met. A common constraint is to specify that a generic type must have a parameterless constructor. However, a natural question arises: can we impose more specific constraints on the constructor?

Case: Forced parameter type

Let's take the example provided in the question, where we want to force a constructor that accepts a float[,] parameter. Initial attempt:

<code class="language-c#">public static T Method<T>(T a) where T : new(float[,] u) {
    //...do something...
    return new T(new float[0, 0]);
}</code>

Compilation failed, forcing us to look for alternatives.

Solution: Create a custom delegate

To circumvent this limitation, we adopted a workaround by introducing a delegate responsible for creating instances of type T. This delegate takes the necessary parameters as parameters and returns an instance of T.

<code class="language-c#">public static void Method<T>(T a, Func<float[,], T> creator) {
    //...do something...
}</code>

Modify our code to use this delegate, with the following results:

<code class="language-c#">A.Method(float[,], instanceCreator);
Func<float[,], T> instanceCreator = (float[,] arr) => new T(arr);</code>

This solution allows us to impose more complex constraints on the constructor by passing in a suitable delegate.

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