In C# can I cast from a T to at T : new()

Question

Here's my code:

void DoSomething<T>()
{
    var constructor = typeof(T).GetConstructor(null);

    if(constructor != null)
    {
        DoSomethingElse<T>(); // compiler error
    }
    else
    {
        //...   
    }

}

void DoSomethingElse<T>() where T:new()
{
   T x = new T();
   //...
}

Is there a way to convince the compiler that T is a legitimate T:new()?

well, no. obviously, the compiler doesn't work that way :) you need to add `new()` constraint to your first method as well. — Selman Genç, Apr 18 '16 at 03:30
Can't. DoSomething needs to work with all types, not just ones that have a default constructor. — Jonathan Allen, Apr 18 '16 at 03:31
hmm then you can try calling `DoSomethingElse` using reflection. — Selman Genç, Apr 18 '16 at 03:32
Does this help you: http://stackoverflow.com/questions/10351385/create-default-instance-of-type — Anil, Apr 18 '16 at 03:33
There is also this post: http://stackoverflow.com/questions/6529611/c-sharp-create-new-t — Anil, Apr 18 '16 at 03:34

Selman Genç · Accepted Answer · 2016-04-18T03:44:23.010

4

There is no way to convince compiler other than adding a new() constraint, if you can't do that the only way is to go with Reflection:

var methodType = // get the type of DoSomethingElse here
var genericMethod = methodType.MakeGenericMethod(typeof(T));

// pass instance instead of null if this is an instance method
genericMethod.Invoke(null);

edited Apr 18 '16 at 03:44

answered Apr 18 '16 at 03:43

Selman Genç

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In C# can I cast from a T to at T : new()

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