[over.ics.user]

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

## 12.2 Overload resolution [[over.match]](over.match#over.ics.user)

### 12.2.4 Best viable function [[over.match.best]](over.match.best#over.ics.user)

#### 12.2.4.2 Implicit conversion sequences [[over.best.ics]](over.best.ics#over.ics.user)

#### 12.2.4.2.3 User-defined conversion sequences [over.ics.user]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L2339)

A [*user-defined conversion sequence*](#def:conversion_sequence,user-defined "12.2.4.2.3 User-defined conversion sequences [over.ics.user]") consists of an initial
standard conversion sequence followed by a user-defined
conversion ([[class.conv]](class.conv "11.4.8 Conversions")) followed by a second standard
conversion sequence[.](#1.sentence-1)

If the user-defined conversion is specified
by a constructor ([[class.conv.ctor]](class.conv.ctor "11.4.8.2 Conversion by constructor")), the initial standard
conversion sequence converts the source type to the type of the
first parameter of that constructor[.](#1.sentence-2)

If the user-defined
conversion is specified by a [conversion function](class.conv.fct "11.4.8.3 Conversion functions [class.conv.fct]"), the
initial standard conversion sequence
converts the source type to the type of the
object parameter of that conversion function[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L2354)

The second standard conversion sequence converts the result of
the user-defined conversion to the target type for the sequence;
any reference binding is included in the second standard
conversion sequence[.](#2.sentence-1)

Since an implicit conversion sequence is an initialization, the
special rules for initialization by user-defined conversion apply
when selecting the best user-defined conversion for a
user-defined conversion sequence (see [[over.match.best]](over.match.best "12.2.4 Best viable function") and [[over.best.ics]](over.best.ics "12.2.4.2 Implicit conversion sequences"))[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L2364)

If the user-defined conversion is specified by a
specialization of a conversion function template,
the second standard conversion sequence shall have Exact Match rank[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/overloading.tex#L2369)

A conversion of an expression of class type
to the same class type is given Exact Match rank, and
a conversion of an expression of class type
to a base class of that type is given Conversion rank,
in spite of the
fact that a constructor (i.e., a user-defined conversion
function) is called for those cases[.](#4.sentence-1)