tmp/tmps32c_92u/{from.md → to.md}
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### Alias templates <a id="temp.alias">[[temp.alias]]</a>
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A *template-declaration* in which the *declaration* is an
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*alias-declaration*
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When a *template-id* refers to the specialization of an alias template,
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it is equivalent to the associated type obtained by substitution of its
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*template-argument*s for the *template-parameter*s in the
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the alias template.
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[*Note 1*: An alias template name is never deduced. — *end note*]
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[*Example 1*:
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@@ -45,19 +45,19 @@ substitution still applies to the *template-id*.
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[*Example 2*:
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``` cpp
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template<typename...> using void_t = void;
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template<typename T> void_t<typename T::foo> f();
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f<int>(); // error
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```
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— *end example*]
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The *type-id* in an alias template declaration shall not refer
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alias template being declared. The type produced by an alias
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specialization shall not directly or indirectly make use of
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specialization.
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[*Example 3*:
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``` cpp
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template <class T> struct A;
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B<short> b; // error: instantiation of B<short> uses own type via A<short>::U
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```
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— *end example*]
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### Alias templates <a id="temp.alias">[[temp.alias]]</a>
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A *template-declaration* in which the *declaration* is an
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*alias-declaration* [[dcl.pre]] declares the *identifier* to be an
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*alias template*. An alias template is a name for a family of types. The
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name of the alias template is a *template-name*.
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When a *template-id* refers to the specialization of an alias template,
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it is equivalent to the associated type obtained by substitution of its
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*template-argument*s for the *template-parameter*s in the
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*defining-type-id* of the alias template.
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[*Note 1*: An alias template name is never deduced. — *end note*]
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[*Example 1*:
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[*Example 2*:
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``` cpp
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template<typename...> using void_t = void;
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template<typename T> void_t<typename T::foo> f();
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f<int>(); // error: int does not have a nested type foo
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```
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— *end example*]
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The *defining-type-id* in an alias template declaration shall not refer
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to the alias template being declared. The type produced by an alias
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template specialization shall not directly or indirectly make use of
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that specialization.
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[*Example 3*:
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``` cpp
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template <class T> struct A;
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B<short> b; // error: instantiation of B<short> uses own type via A<short>::U
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```
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— *end example*]
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The type of a *lambda-expression* appearing in an alias template
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declaration is different between instantiations of that template, even
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when the *lambda-expression* is not dependent.
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[*Example 4*:
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``` cpp
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template <class T>
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using A = decltype([] { }); // A<int> and A<char> refer to different closure types
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```
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— *end example*]
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