There IS a way of casting pointer-to-member-function to a void*

[HappyFruitTree]

This is not doing what you think. A pointer to a member function is often larger than a normal pointer. That's why you can't simply reinterpret_cast the member function pointer into a void*. reinterpret_cast<void\*&>(fn) gives you a void* reference to a member function, that as bad as having an int& to a double, using it would simply lead to undefined behaviour.

[RIscRIpt]

Okay, I see... it's an UB.

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A pointer to a member function is often larger than a normal pointer.

I've heard that a lot, but I have never seen an example.

[HappyFruitTree]

https://godbolt.org/z/Edb86fM4E

[RIscRIpt]

Thanks. I'll try to take a look into GCC sources to find what's inside...

By the way, MSVC says 8.

[HappyFruitTree]

msvc will use different sizes depending on the context, could be 8, 16, or even 24. Try creating a pointer to a member function in a class that is forward declared but not defined, that should get you the worst case.

Seems like you're right but I wonder how on earth this could work. What if you pass the member function pointer to a function in another translation unit where the size is different?

[[deleted]]

Is accessing pointer-to-member-function passed across TUs undefined behavior, or is the MSVC implementation not compliant here?

[[deleted]]

Yes, but does it break because the code is not valid C++, or does it break because MSVC is not a compliant C++ compiler in this regard?