Structs, Interfaces and Boxing [duplicate]

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Jon’s point is true, but as a side note there is one slight exception to the rule; generics. If you have where T : ISomeInterface, then this is constrained, and uses a special opcode. This means the interface can be used without boxing. For example:

public static void Foo<T>(T obj) where T : ISomeInterface {
    obj.Bar(); // Bar defined on ISomeInterface
}

This does not involve boxing, even for value-type T. However, if (in the same Foo) you do:

ISomeInterface asInterface = obj;
asInterface.Bar();

then that boxes as before. The constrained only applies directly to T.

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