Question

 public class TwitterResponse<T>
        where T : Core.ITwitterObject
    {
       // all properties and methods here
    }

Can someone explain me what is this in simple terms ? what is “where T :Core.ITwitterObject ” part here ? Have seen this in Twitterizer source code. Any examples to better understand this ?

Answer 1

This means that T must implement interface Core.ITwitterObject.

If you pass to the generic a type T not implementing this interface, a compile-time error occurs.

This condition allows the compiler to call the functions which are declared in Core.ITwitterObject on instances of T.

Look at the documentation for more information.

Example:

interface IFoo { void Perform(); }

class FooList<T> where T : IFoo
{
    List<T> foos;
    ...
    void PerformForAll()
    {
        foreach (T foo in foos)
            foo.Perform(); // this line compiles because the compiler knows
                           // that T implements IFoo
    }
}

This has an advantage over the customary

interface IFoo { void Perform(); }

class FooList
{
    List<IFoo> foos;
    ...
    void PerformForAll()
    {
        foreach (IFoo foo in foos)
            foo.Perform();
    }
    // added example method
    IFoo First { get { return foos[0]; } }
}

because the methods like First would be more type-safe, you won’t need to downcast from IFoo to SomeRandomFooImpl.