tmp/tmpc17te38q/{from.md → to.md}
RENAMED
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@@ -17,22 +17,26 @@ conversion-type-id:
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conversion-declarator:
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ptr-operator conversion-declaratorₒₚₜ
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```
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specifies a conversion from `X` to the type specified by the
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*conversion-type-id*. Such functions are called conversion functions.
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reference to it), or to
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``` cpp
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struct X {
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operator int();
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};
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void f(X a) {
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int i = int(a);
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i = (int)a;
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@@ -41,16 +45,20 @@ void f(X a) {
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```
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In all three cases the value assigned will be converted by
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`X::operator int()`.
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A conversion function may be explicit ([[dcl.fct.spec]]), in which case
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it is only considered as a user-defined conversion for
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direct-initialization ([[dcl.init]]). Otherwise, user-defined
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conversions are not restricted to use in assignments and
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initializations.
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``` cpp
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class Y { };
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struct Z {
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explicit operator Y() const;
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};
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@@ -67,25 +75,60 @@ void g(X a, X b) {
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if (a) {
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}
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}
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```
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The *conversion-type-id* shall not represent a function type nor an
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array type. The *conversion-type-id* in a *conversion-function-id* is
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the longest
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``` cpp
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&ac.operator int*i; // syntax error:
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// parsed as: &(ac.operator int *)i
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// not as: &(ac.operator int)*i
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```
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The `*` is the pointer declarator and not the multiplication operator.
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Conversion functions are inherited.
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Conversion functions can be virtual.
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conversion-declarator:
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ptr-operator conversion-declaratorₒₚₜ
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```
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specifies a conversion from `X` to the type specified by the
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*conversion-type-id*. Such functions are called *conversion functions*.
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A *decl-specifier* in the *decl-specifier-seq* of a conversion function
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(if any) shall be neither a *defining-type-specifier* nor `static`. The
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type of the conversion function ([[dcl.fct]]) is “function taking no
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parameter returning *conversion-type-id*”. A conversion function is
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never used to convert a (possibly cv-qualified) object to the (possibly
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cv-qualified) same object type (or a reference to it), to a (possibly
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cv-qualified) base class of that type (or a reference to it), or to
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(possibly cv-qualified) void.[^2]
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[*Example 1*:
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``` cpp
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struct X {
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operator int();
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operator auto() -> short; // error: trailing return type
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};
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void f(X a) {
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int i = int(a);
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i = (int)a;
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```
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In all three cases the value assigned will be converted by
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`X::operator int()`.
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— *end example*]
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A conversion function may be explicit ([[dcl.fct.spec]]), in which case
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it is only considered as a user-defined conversion for
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direct-initialization ([[dcl.init]]). Otherwise, user-defined
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conversions are not restricted to use in assignments and
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initializations.
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[*Example 2*:
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``` cpp
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class Y { };
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struct Z {
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explicit operator Y() const;
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};
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if (a) {
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}
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}
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```
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— *end example*]
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The *conversion-type-id* shall not represent a function type nor an
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array type. The *conversion-type-id* in a *conversion-function-id* is
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the longest sequence of tokens that could possibly form a
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*conversion-type-id*.
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[*Note 1*:
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This prevents ambiguities between the declarator operator `*` and its
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expression counterparts.
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[*Example 3*:
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``` cpp
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&ac.operator int*i; // syntax error:
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// parsed as: &(ac.operator int *)i
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// not as: &(ac.operator int)*i
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```
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The `*` is the pointer declarator and not the multiplication operator.
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— *end example*]
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This rule also prevents ambiguities for attributes.
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[*Example 4*:
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``` cpp
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operator int [[noreturn]] (); // error: noreturn attribute applied to a type
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```
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— *end example*]
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— *end note*]
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Conversion functions are inherited.
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Conversion functions can be virtual.
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A conversion function template shall not have a deduced return type (
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[[dcl.spec.auto]]).
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[*Example 5*:
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``` cpp
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struct S {
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operator auto() const { return 10; } // OK
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template<class T>
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operator auto() const { return 1.2; } // error: conversion function template
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};
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```
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— *end example*]
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