Question

I have a research about feature “Data Access Application Block” in EntLib. I find some codes:

public static class MapBuilder<TResult> where TResult : new()
{
    //...
}

I don’t understand about meaning of declaring of this class when using “where TResult : new()“. I think this is new feature in .NET Framework to declare a class. Please give me a document or link to explain about this feature. Thanks.

Answer 1

It’s a generic type parameter constraint. It’s been around since the introduction of generics, in .net 2.0.

Constraints on Type Parameters (MSDN)

The particular constraint you’ve mentioned means only a class with a public parameterless constructor can be used as the type TResult.

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See also: Generics (MSDN)