371.md

Info

• Did you know that C++26 added = delete("should have a reason")?

  • https://wg21.link/P2573

Example

void newapi();
void oldapi() = delete("This old API is outdated and already been removed. Please use newapi() instead.");

int main () {
  oldapi();
}

https://godbolt.org/z/aPz1bM4x6

Puzzle

• Can you implment simplified addressof with delete("Cannot take address of rvalue.") when used incorreclty?

// TODO addressof

int main() {
  int i{};
  addressof(i);     // okay
  addressof(int{}); // error: "Cannot take address of rvalue."
}

https://godbolt.org/z/M6881vY65

Solutions

template<class T> constexpr T* addressof(T& r) noexcept { return &r; }
template<class T> const T* addressof(const T&&) = delete("Cannot take address of rvalue.");

int main() {
  int i{};
  addressof(i);     // okay
  addressof(int{}); // error: "Cannot take address of rvalue."
}

https://godbolt.org/z/hMYWThGxj