12 Overloading [over]

12.2 Overload resolution [over.match]

12.2.2 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”, conversion functions are considered.
    The permissible types for non-explicit conversion functions are T and any class derived from T.
    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”, the permissible types for explicit conversion functions are the same; otherwise there are none.
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 object parameter of the conversion functions.
— end note]