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c#genericsconstraints
Andrei V
Andrei V

Reputation: 7506

Is it pointless to have both "class" and "new()" constraints in a generic class?

I am wondering if it makes any sense to have both "class" and "new()" constraints when defining a generic class. As in the following example:

class MyParanoidClass<T> where T : class, new()
{
 //content
}

Both constraints specify that T should be a reference type. While the "class" constraint does not imply that a implicit constructor exists, the "new()" constraint does require a "class" with an additional public constructor definition.

My final (formulation for the) question is: do I have any benefits from defining a generic class as in the above statement, or does "new()" encapsulate both constraints?

Upvotes: 5

Views: 324

Answers (2)

Ehsan
Ehsan

Reputation: 32681

No they are not useless.

First parameter class ensures that the type argument must be a reference type, including any class, interface, delegate, or array type,

whereas second parameter new() ensures that it has a parameter less default constructor. It will not work for any class that doesn't have parameter less default constructor.

Upvotes: 1

Daniel Hilgarth
Daniel Hilgarth

Reputation: 174329

new() doesn't imply a reference type, so: No, class is not redundant when using new().

The following code demonstrates that:

void Main()
{
    new MyParanoidClass<S>();
}

struct S {}

class MyParanoidClass<T> where T : new()
{
    //content
}

This code compiles, proving that new() doesn't care if you use a reference or a value type.

Upvotes: 7

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