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A subtlety with using pointers to members in combination with
reference bindings was observed by Mike
Spertus. Consider the following example in which a const member function
tt(fun) was declared with a reference token tt(&):
verb( struct Demo
{
void fun() const &;
};)
Although tt(fun) was declared with a tt(&) reference token, it can
nevertheless be called from an anonymous (rvalue) tt(Demo) object, because
it's a const member function:
verb( Demo{}.fun(); // OK since C++20)
However, up to the C++20 standard this function could not be called
using a pointer-to-member construction from an anonymous tt(Demo)
object. This inconsistency was removed in the C++20 standard, allowing
the following statements to be correctly compiled:
verb( (Demo{}.*&Demo::fun)(); // using .* and fun's address
// pf receives fun's address
void (Demo::*pf)() const & = &Demo::fun;
(Demo{}.*pf)(); // call fun via the pointer pf)
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