What does the class type constraint achieve if a generic type constraint must also implement an interface in c#

Question

When writing generic methods and functions, I have seen the Where type constraint written as

public static void MyMethod<T>(params T[] newVals) where T : IMyInterface

and also

public static void MyMethod<T>(params T[] newVals) where T : class, IMyInterface

does the 'class' type constraint add anything - I don't imagine a struct could ever implement an interface, but i could be wrong?

Thank you

Yes, structs can implement interfaces. See : [Int32 Structure](http://msdn.microsoft.com/en-us/library/system.int32(v=vs.110).aspx) — Selman Genç, Jul 09 '14 at 22:14
`Enumerator` is an example of a struct that implements an interface. http://stackoverflow.com/questions/521298/when-to-use-struct-in-c — Tom Chantler, Jul 09 '14 at 22:14

score 2 · Accepted Answer · answered Jul 09 '14 at 22:16

A struct can implement an interface, so it's quite reasonable to have the double constraint of requiring the generic type T to be both a class and to implement the specified interface.

Consider this from Dictionary:

[Serializable, StructLayout(LayoutKind.Sequential)]
public struct Enumerator : 
    IEnumerator<KeyValuePair<TKey, TValue>>, IDisposable, 
    IDictionaryEnumerator, IEnumerator
{
    //  use Reflector to see the code
}

score 1 · Answer 2 · answered Jul 09 '14 at 22:15

1

Structs can implement interfaces. So this

where T : class, IMyInterface

demands both the type T be a class and a class which implements the interface called IMyInterface.

For instance this is the declaration of Int32 structure:

[SerializableAttribute]
[ComVisibleAttribute(true)]
public struct Int32 : IComparable, IFormattable, 
                      IConvertible, IComparable<int>, IEquatable<int>

as you can see here.

answered Jul 09 '14 at 22:15

Christos

53,228
8
76
108

Thank you - I would have marked you as answer (both answers with clear examples of where my assumption was wrong), but Dommer got in 1 min earlier – Brent Jul 09 '14 at 22:33
@Brent not a problem dude. – Christos Jul 09 '14 at 22:34

What does the class type constraint achieve if a generic type constraint must also implement an interface in c#

2 Answers2