C++ vs. C++/CLI: Const qualification of virtual function parameters

Question

[All of the following was tested using Visual Studio 2008 SP1]

In C++, const qualification of parameter types does not affect the type of a function (8.3.5/3: "

Answer 1

Well, it's a bug. The const modifiers is emitted into the metadata with the modopt custom modifier. Unfortunately, the C++/CLI language rules do not match the CLI rules. Chapter 7.1.1 of the CLI spec says:

Custom modifiers, defined using modreq (“required modifier”) and modopt (“optional modifier”), are similar to custom attributes (§21) except that modifiers are part of a signature rather than being attached to adeclaration. Each modifer associates a type reference with an item in the signature.

The CLI itself shall treat required and optional modifiers in the same manner. Two signatures that differ only by the addition of a custom modifier (required or optional) shall not be considered to match. Custom modifiers have no other effect on the operation of the VES.

So, the CLR says that Derived::Foo() is not a override, C++/CLI says it is. The CLR wins.

You could report the bug at connect.microsoft.com but it probably a waste of time. I think this incompatibility was intentional. They should have changed the language rules for C++/CLI but surely thought C++ compatibility to be more important. CV modifiers are a pain anyway, there are other scenarios that are not well supported, const pointers to const for one. This cannot be enforced at runtime anyway, the CLR has no support for it.