12 Overloading [over]

12.4 Overload resolution [over.match]

12.4.2 Candidate functions and argument lists [over.match.funcs] Copy-initialization of class by user-defined conversion [over.match.copy]

Under the conditions specified in [dcl.init], as part of a copy-initialization of an object of class type, a user-defined conversion can be invoked to convert an initializer expression to the type of the object being initialized.
Overload resolution is used to select the user-defined conversion to be invoked.
[Note 1:
The conversion performed for indirect binding to a reference to a possibly cv-qualified class type is determined in terms of a corresponding non-reference copy-initialization.
— end note]
Assuming that “cv1 T” is the type of the object being initialized, with T a class type, the candidate functions are selected as follows:
  • The converting constructors of T are candidate functions.
  • When the type of the initializer expression is a class type “cv S”, the non-explicit conversion functions of S and its base classes are considered.
    When initializing a temporary object ([class.mem]) to be bound to the first parameter of a constructor where the parameter is of type “reference to cv2 T” and the constructor is called with a single argument in the context of direct-initialization of an object of type “cv3 T”, explicit conversion functions are also considered.
    Those that are not hidden within S and yield a type whose cv-unqualified version is the same type as T or is a derived class thereof are candidate functions.
    A call to a conversion function returning “reference to X” is a glvalue of type X, and such a conversion function is therefore considered to yield X for this process of selecting candidate functions.
In both cases, the argument list has one argument, which is the initializer expression.
[Note 2:
This argument will be compared against the first parameter of the constructors and against the implicit object parameter of the conversion functions.
— end note]