Fix the way we trigger an error on Kaleidoscope.use() with V2 API

[algernon]

When using Kaleidoscope.use() and the V1 API is disabled, we want to display an error. The current method of doing that is not reliable, it sometimes works, sometimes will error out even when not using Kaleidoscope.use(). To fix this, make the assert a tiny bit more complicated, so that the compiler won't act too smart.

(Note: I'm not entirely sure why this works, but it appears to do the trick.)

[noseglasses]

I'm not entirely sure why this works, but it appears to do the trick

Your solution is called deferred instantiation. In your original version the compiler could evaluate the static_assert right away and it would always fire. The modified version requires the Plugin__ template argument to be known, which deferrs the evaluation of the static_assert until the use template function is instanciated.

You could write the whole thing a bit shorter, without always_false as

template <typename Plugin__>
inline void use(Plugin__ first, ...) {
    static_assert(sizeof(Plugin__) < 0, _DEPRECATE(_DEPRECATED_MESSAGE_USE));
}

In this version the sizeof-operator and thus the static_assert can also not be evaluated until Plugin__ becomes known during instanciation of use. Of course the expression sizeof(Plugin__) < 0 is always false.

[algernon]

Thanks! I managed to figure out the why, but it's great to know the name, too. And the simplification is <3, will update this PR and MagicCombo too.

Much appreciated!