[over.match.general]

# 12 Overloading [[over]](./#over)

## 12.2 Overload resolution [[over.match]](over.match#general)

### 12.2.1 General [over.match.general]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L49)

Overload resolution is a mechanism for selecting the best
function to call given a list of expressions that are to be the
arguments of the call and a set of[*candidate functions*](#def:candidate "12.2.1 General [over.match.general]") that can
be called based on the context of the call[.](#1.sentence-1)

The selection
criteria for the best function are the number of arguments, how
well the arguments match the parameter-type-list of the
candidate function,
how well (for non-static member functions) the object
matches the object parameter,
and certain other properties of the candidate function[.](#1.sentence-2)

[*Note [1](#note-1)*:

The function selected by overload resolution is not
guaranteed to be appropriate for the context[.](#1.sentence-3)

Other restrictions,
such as the accessibility of the function, can make its use in
the calling context ill-formed[.](#1.sentence-4)

— *end note*]

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L71)

Overload resolution selects the function to call in seven distinct
contexts within the language:

- [(2.1)](#2.1)

invocation of a function named in the [function call syntax](over.call.func "12.2.2.2.2 Call to designated function [over.call.func]");

- [(2.2)](#2.2)

invocation of a function call operator, a pointer-to-function
conversion function, a reference-to-pointer-to-function conversion
function, or a reference-to-function
conversion function on a class object named in the function
call syntax ([[over.call.object]](over.call.object "12.2.2.2.3 Call to object of class type"));

- [(2.3)](#2.3)

invocation of the operator referenced in an expression ([[over.match.oper]](over.match.oper "12.2.2.3 Operators in expressions"));

- [(2.4)](#2.4)

invocation of a constructor for default- or direct-initialization ([[dcl.init]](dcl.init "9.5 Initializers"))
of a class object ([[over.match.ctor]](over.match.ctor "12.2.2.4 Initialization by constructor"));

- [(2.5)](#2.5)

invocation of a user-defined conversion for[copy-initialization](dcl.init#def:copy-initialization "9.5 Initializers [dcl.init]") of a class object ([[over.match.copy]](over.match.copy "12.2.2.5 Copy-initialization of class by user-defined conversion"));

- [(2.6)](#2.6)

invocation of a conversion function for initialization of an object of a
non-class type from an expression of class type ([[over.match.conv]](over.match.conv "12.2.2.6 Initialization by conversion function")); and

- [(2.7)](#2.7)

invocation of a conversion function for conversion
in which a reference ([[dcl.init.ref]](dcl.init.ref "9.5.4 References"))
will be [directly bound](over.match.ref "12.2.2.7 Initialization by conversion function for direct reference binding [over.match.ref]")[.](#2.sentence-1)

Each of these contexts defines the set of candidate functions and
the list of arguments in its own unique way[.](#2.sentence-2)

But, once the
candidate functions and argument lists have been identified, the
selection of the best function is the same in all cases:

- [(2.8)](#2.8)

  First, a subset of the candidate functions (those that have
the proper number of arguments and meet certain other
conditions) is selected to form a set ofviable functions ([[over.match.viable]](over.match.viable "12.2.3 Viable functions"))[.](#2.8.sentence-1)

- [(2.9)](#2.9)

  Then the best viable function is selected based on the[implicit conversion sequences](over.best.ics "12.2.4.2 Implicit conversion sequences [over.best.ics]") needed to
match each argument to the corresponding parameter of each
viable function[.](#2.9.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L120)

If a best viable function exists and is unique, overload
resolution succeeds and produces it as the result[.](#3.sentence-1)

Otherwise
overload resolution fails and the invocation is ill-formed[.](#3.sentence-2)

When overload resolution succeeds,
and the best viable function is not [accessible](class.access "11.8 Member access control [class.access]") in the context
in which it is used,
the program is ill-formed[.](#3.sentence-3)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L130)

Overload resolution results in a [*usable candidate*](#def:candidate,usable "12.2.1 General [over.match.general]") if overload resolution succeeds and
the selected candidate
is either not a function ([[over.built]](over.built "12.5 Built-in operators")), or
is a function that is not deleted and
is accessible from the context
in which overload resolution was performed[.](#4.sentence-1)