In C#, one is allowed to write:
public class Foo<T> where T : class {
}
And according to the C# specifications, this means that:
The type argument must be a reference type; this applies also to any class, interface, delegate, or array type.
Some are of the opinion that the literal statement T : class is confusing, one could see it as.
The type argument must be a class type. So interfaces and delegates are not allowed. (wrong)
Where for instances interfaces and delegates are not allowed. I'm wondering if the C# design team considered this and why they didn't introduce a constraint like:
where T : reference
(Or another keyword that is more precise). What was the rationale to use : class instead?
They wanted to stick to a keyword that was already present in the language. Surely reference or referencetype would be more precise.
Similarly, it is called where T : struct, not valuetype (or nonnullablevaluetype), even if both structs and enums are value types that can be used for T in that case. Also note that the special struct Nullable<> is not allowed if the constraint where T : struct was used.