What means where S : new() in c# [duplicate]

Question

In the following code I do not know what means " where S : new() " part. What is the keyword to find more info in Google ?

    public virtual void Print<S, T>() 
        where S : new() 
    { 
        Console.WriteLine(default(T)); 
        Console.WriteLine(default(S)); 
    } 

Answer 1

The new() constraint means that the particular generic parameter is required to have a default constructor (i. e. a constructor with no parameters).

The purpose of this is typically to allow you to type-safely construct new instances of generic parameter types without resorting to reflection/Activator.CreateInstance.

For example:

public T Create<T>() where T : new()
{
    // allowed because of the new() constraint
    return new T();
}

For more information, check out http://msdn.microsoft.com/en-us/library/sd2w2ew5%28v=vs.80%29.aspx.

As far as a google search term, I'd try "c# new() constraint".