如果泛型类型约束还必须在c＃中实现接口，那么类类型约束会实现什么？

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

Answer 1

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
}

Answer 2

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 .