12 Overloading [over]

12.2 Overload resolution [over.match]

12.2.2 Candidate functions and argument lists [over.match.funcs]

12.2.2.7 Initialization by conversion function for direct reference binding [over.match.ref]

1
#
Under the conditions specified in [dcl.init.ref], a reference can be bound directly to the result of applying a conversion function to an initializer expression.
Overload resolution is used to select the conversion function to be invoked.
Assuming that β€œreference to cv1 T” is the type of the reference being initialized, the candidate functions are selected as follows:
  • (1.1)
    Let R be a set of types including
    • (1.1.1)
      β€œlvalue reference to cv2 T2” (when initializing an lvalue reference or an rvalue reference to function) and
    • (1.1.2)
      β€œcv2 T2” and β€œrvalue reference to cv2 T2” (when initializing an rvalue reference or an lvalue reference to function)
    for any T2.
    The permissible types for non-explicit conversion functions are the members of R where β€œcv1 T” is reference-compatible ([dcl.init.ref]) with β€œcv2 T2”.
    For direct-initialization, the permissible types for explicit conversion functions are the members of R where T2 can be converted to type T with a (possibly trivial) qualification conversion ([conv.qual]); otherwise there are none.
2
#
The argument list has one argument, which is the initializer expression.
[Note 1: 
This argument will be compared against the object parameter of the conversion functions.
β€” end note]