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c#.netgenericstype-constraints
Meryovi
Meryovi

Reputation: 6231

C# generic methods, type parameters in new() constructor constraint

Is there a way to create a Generic Method that uses the new() constraint to require classes with constructor attributes of specific types?

For Example:

I have the following code:

public T MyGenericMethod<T>(MyClass c) where T : class
{
    if (typeof(T).GetConstructor(new Type[] { typeof(MyClass) }) == null)
    {
        throw new ArgumentException("Invalid class supplied");
    }
    // ...
}

Is it possible to have something like this instead?

public T MyGenericMethod<T>(MyClass c) where T : new(MyClass)
{
    // ...
}

EDIT: There's a suggestion regarding this. Please vote so we can have this feature in C#!

EDIT 2: The site has been taken down. Now the suggestion is on Github. Follow up there!

Upvotes: 26

Views: 9069

Answers (3)

thecoop
thecoop

Reputation: 46098

Not really; C# only supports no-args constructor constraints.

The workaround I use for generic arg constructors is to specify the constructor as a delegate:

public T MyGenericMethod<T>(MyClass c, Func<MyClass, T> ctor) {
    // ...
    T newTObj = ctor(c);
    // ...
}

then when calling:

MyClass c = new MyClass();
MyGenericMethod<OtherClass>(c, co => new OtherClass(co));

Upvotes: 35

driis
driis

Reputation: 164291

No, it is not possible in C# to constrain the generic type to have a constructor of a specific signature. Only the parameterless constructor is supported by new().

Upvotes: 3

Reed Copsey
Reed Copsey

Reputation: 564413

No. Unfortunately, generic constraints only allow you to include:

where T : new()

Which specifies that there is a default, parameterless constructor. There is no way to constrain to a type with a constructor which accepts a specific parameter type.

For details, see Constraints on Type Parameters.

Upvotes: 9

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