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| <h3 class="section">7.9 Type Traits</h3> |
| |
| <p>The C++ front-end implements syntactic extensions that allow to |
| determine at compile time various characteristics of a type (or of a |
| pair of types). |
| |
| <dl> |
| <dt><code>__has_nothrow_assign (type)</code><dd>If <code>type</code> is const qualified or is a reference type then the trait is |
| false. Otherwise if <code>__has_trivial_assign (type)</code> is true then the trait |
| is true, else if <code>type</code> is a cv class or union type with copy assignment |
| operators that are known not to throw an exception then the trait is true, |
| else it is false. Requires: <code>type</code> shall be a complete type, an array |
| type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_nothrow_copy (type)</code><dd>If <code>__has_trivial_copy (type)</code> is true then the trait is true, else if |
| <code>type</code> is a cv class or union type with copy constructors that |
| are known not to throw an exception then the trait is true, else it is false. |
| Requires: <code>type</code> shall be a complete type, an array type of |
| unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_nothrow_constructor (type)</code><dd>If <code>__has_trivial_constructor (type)</code> is true then the trait is |
| true, else if <code>type</code> is a cv class or union type (or array |
| thereof) with a default constructor that is known not to throw an |
| exception then the trait is true, else it is false. Requires: |
| <code>type</code> shall be a complete type, an array type of unknown bound, |
| or is a <code>void</code> type. |
| |
| <br><dt><code>__has_trivial_assign (type)</code><dd>If <code>type</code> is const qualified or is a reference type then the trait is |
| false. Otherwise if <code>__is_pod (type)</code> is true then the trait is |
| true, else if <code>type</code> is a cv class or union type with a trivial |
| copy assignment ([class.copy]) then the trait is true, else it is |
| false. Requires: <code>type</code> shall be a complete type, an array type |
| of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_trivial_copy (type)</code><dd>If <code>__is_pod (type)</code> is true or <code>type</code> is a reference type |
| then the trait is true, else if <code>type</code> is a cv class or union type |
| with a trivial copy constructor ([class.copy]) then the trait |
| is true, else it is false. Requires: <code>type</code> shall be a complete |
| type, an array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_trivial_constructor (type)</code><dd>If <code>__is_pod (type)</code> is true then the trait is true, else if |
| <code>type</code> is a cv class or union type (or array thereof) with a |
| trivial default constructor ([class.ctor]) then the trait is true, |
| else it is false. Requires: <code>type</code> shall be a complete type, an |
| array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_trivial_destructor (type)</code><dd>If <code>__is_pod (type)</code> is true or <code>type</code> is a reference type then |
| the trait is true, else if <code>type</code> is a cv class or union type (or |
| array thereof) with a trivial destructor ([class.dtor]) then the trait |
| is true, else it is false. Requires: <code>type</code> shall be a complete |
| type, an array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__has_virtual_destructor (type)</code><dd>If <code>type</code> is a class type with a virtual destructor |
| ([class.dtor]) then the trait is true, else it is false. Requires: |
| <code>type</code> shall be a complete type, an array type of unknown bound, |
| or is a <code>void</code> type. |
| |
| <br><dt><code>__is_abstract (type)</code><dd>If <code>type</code> is an abstract class ([class.abstract]) then the trait |
| is true, else it is false. Requires: <code>type</code> shall be a complete |
| type, an array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__is_base_of (base_type, derived_type)</code><dd>If <code>base_type</code> is a base class of <code>derived_type</code> |
| ([class.derived]) then the trait is true, otherwise it is false. |
| Top-level cv qualifications of <code>base_type</code> and |
| <code>derived_type</code> are ignored. For the purposes of this trait, a |
| class type is considered is own base. Requires: if <code>__is_class |
| (base_type)</code> and <code>__is_class (derived_type)</code> are true and |
| <code>base_type</code> and <code>derived_type</code> are not the same type |
| (disregarding cv-qualifiers), <code>derived_type</code> shall be a complete |
| type. Diagnostic is produced if this requirement is not met. |
| |
| <br><dt><code>__is_class (type)</code><dd>If <code>type</code> is a cv class type, and not a union type |
| ([basic.compound]) the trait is true, else it is false. |
| |
| <br><dt><code>__is_empty (type)</code><dd>If <code>__is_class (type)</code> is false then the trait is false. |
| Otherwise <code>type</code> is considered empty if and only if: <code>type</code> |
| has no non-static data members, or all non-static data members, if |
| any, are bit-fields of length 0, and <code>type</code> has no virtual |
| members, and <code>type</code> has no virtual base classes, and <code>type</code> |
| has no base classes <code>base_type</code> for which |
| <code>__is_empty (base_type)</code> is false. Requires: <code>type</code> shall |
| be a complete type, an array type of unknown bound, or is a |
| <code>void</code> type. |
| |
| <br><dt><code>__is_enum (type)</code><dd>If <code>type</code> is a cv enumeration type ([basic.compound]) the trait is |
| true, else it is false. |
| |
| <br><dt><code>__is_pod (type)</code><dd>If <code>type</code> is a cv POD type ([basic.types]) then the trait is true, |
| else it is false. Requires: <code>type</code> shall be a complete type, |
| an array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__is_polymorphic (type)</code><dd>If <code>type</code> is a polymorphic class ([class.virtual]) then the trait |
| is true, else it is false. Requires: <code>type</code> shall be a complete |
| type, an array type of unknown bound, or is a <code>void</code> type. |
| |
| <br><dt><code>__is_union (type)</code><dd>If <code>type</code> is a cv union type ([basic.compound]) the trait is |
| true, else it is false. |
| |
| </dl> |
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