Extended Description

Today's trunk and release/10.x accept the TU:

  struct ExplicitToInt {
    explicit operator int() const;
  };

  const int& x(ExplicitToInt{}); // #1
  int&& y(ExplicitToInt{});      // #2

despite that GCC, MSVC, and I agree that both reference bindings are ill-formed. Running quickly through the bullets in [dcl.init.ref]/5:

• 5.1 doesn't apply: the initializer is not an lvalue

• 5.2 doesn't apply: neither target reference is an lvalue reference to non-const-qualified or volatile-qualified type

• 5.3.1 doesn't apply: Neither int nor const int is reference-compatible with ExplicitToInt

• 5.3.2: doesn't apply, assuming that "can be converted" means "can be implicitly converted"

• 5.4: doesn't apply because the explicit conversion operator cannot be selected for "copy-initialization of an object of type "cv1 T1" [const int and int for #1 and #2 respectively] by user-defined conversion".