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std::common_type

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Grundtypen
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Basic types
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Grundtypen
Feste Breite Integer-Typen (C++11)
Numerische Grenzen
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Numeric limits
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numeric_limits
C numerische begrenzt Schnittstelle
Laufzeit-Typinformationen
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Runtime type information
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Exterieur
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Type traits
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Primären Typ Kategorien
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Primary type categories
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is_void(C++11)
is_array(C++11)
is_pointer(C++11)
is_enum(C++11)
is_union(C++11)
is_class(C++11)
is_function(C++11)
is_object(C++11)
is_scalar(C++11)
is_compound(C++11)
is_integral(C++11)
is_floating_point(C++11)
is_fundamental(C++11)
is_arithmetic(C++11)
is_reference(C++11)
is_lvalue_reference(C++11)
is_rvalue_reference(C++11)
is_member_pointer(C++11)
is_member_object_pointer(C++11)
is_member_function_pointer(C++11)
Typ Eigenschaften
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Type properties
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is_const(C++11)
is_volatile(C++11)
is_pod(C++11)
is_empty(C++11)
is_polymorphic(C++11)
is_abstract(C++11)
Unterstützte Operationen
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Supported operations
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is_constructible
is_trivially_constructible
is_nothrow_constructible
(C++11)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible
(C++11)
(C++11)
(C++11)
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible
(C++11)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible
(C++11)
(C++11)
(C++11)
is_assignable
is_trivially_assignable
is_nothrow_assignable
(C++11)
(C++11)
(C++11)
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable
(C++11)
(C++11)
(C++11)
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable
(C++11)
(C++11)
(C++11)
is_destructible
is_trivially_destructible
is_nothrow_destructible
(C++11)
(C++11)
(C++11)
has_virtual_destructor(C++11)
Beziehungen und Eigentum Abfragen
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Relationships and property queries
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is_same(C++11)
is_base_of(C++11)
is_convertible(C++11)
alignment_of(C++11)
rank(C++11)
extent(C++11)
Typ Modifikationen
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Type modifications
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remove_cv
remove_const
remove_volatile
(C++11)
(C++11)
(C++11)
add_cv
add_const
add_volatile
(C++11)
(C++11)
(C++11)
make_signed(C++11)
make_unsigned(C++11)
Typ Transformationen
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Type transformations
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aligned_storage(C++11)
aligned_union(C++11)
decay(C++11)
enable_if(C++11)
conditional(C++11)
common_type(C++11)
underlying_type(C++11)
result_of(C++11)
Typ-Trait-Konstanten
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Type trait constants
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integral_constant(C++11)
 
Defined in header <type_traits>
template< class... T >
struct common_type;
(seit C++11)
Bestimmt die häufigste Art unter allen Typen T..., das ist die Art all T... implizit konvertiert werden können .
Original:
Determines the common type among all types T..., that is the type all T... can be implicitly converted to.
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  • std::common_type kann für benutzerdefinierte Typen, z. B. spezialisiert werden std::chrono::time_point .
    Original:
    std::common_type may be specialized for custom types, e.g. std::chrono::time_point.
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  • Für nicht-spezialisierten std::common_type, die Regeln für die Bestimmung der häufigste Art zwischen jedem Paar T1, T2 sind genau die Regeln für die Bestimmung der Rückgabetyp der dreifach konditionalen Operator wo T1 und T2 sind die Arten der zweiten und dritten Operanden .
    Original:
    For non-specialized std::common_type, the rules for determining the common type between every pair T1, T2 are exactly the rules for determining the return type of the dreifach konditionalen Operator where T1 and T2 are the types of its second and the third operands.
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  • Für arithmetische Typen kann der gemeinsame Typ auch als Typ der (allenfalls Mixed-Mode) arithmetischer Ausdruck wie T0() + T1() + ... + Tn() angesehen werden .
    Original:
    For arithmetic types, the common type may also be viewed as the type of the (possibly mixed-mode) arithmetic expression such as T0() + T1() + ... + Tn().
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Inhaltsverzeichnis

[Bearbeiten] Mitglied Typen

Name
Original:
Name
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Definition
type
die häufigste Art für alle T...
Original:
the common type for all T...
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[Bearbeiten] Spezialisierungen

Benutzerdefinierte Spezialisierungen des Typs trait std::common_type sind erlaubt. Die folgenden Spezialisierungen sind bereits von der Standard-Bibliothek zur Verfügung:
Original:
Custom specializations of the type trait std::common_type are allowed. The following specializations are already provided by the standard library:
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spezialisiert die std::common_type Merkmal
Original:
specializes the std::common_type trait
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(class Template-Spezialisierung) [edit]
spezialisiert die std::common_type Merkmal
Original:
specializes the std::common_type trait
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(class Template-Spezialisierung) [edit]

[Bearbeiten] Notes

Mit einem einzigen Template-Argument ist std::common_type<T>::type genau T, die es der C + + entspricht boost::identity<T> macht
Original:
With a single template argument, std::common_type<T>::type is exactly T, which makes it the C++ equivalent of boost::identity<T>
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[Bearbeiten] Mögliche Implementierung

template<class ...T> struct common_type;
 
template<class T>
struct common_type<T> {
    typedef T type;
};
 
template<class T, class U>
struct common_type<T, U> {
    typedef decltype(true ? declval<T>() : declval<U>()) type;
};
 
template<class T, class U, class... V>
struct common_type<T, U, V...> {
    typedef typename common_type<typename common_type<T, U>::type, V...>::type type;
};

[Bearbeiten] Beispiel

Demonstriert, Mixed-Mode-Arithmetik auf einer benutzerdefinierten Klasse
Original:
Demonstrates mixed-mode arithmetic on a user-defined class
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#include <iostream>
#include <type_traits>
 
template<class T>
struct Number { T n; };
 
template<class T, class U>
Number<typename std::common_type<T, U>::type> operator+(const Number<T>& lhs,
                                                        const Number<U>& rhs) 
{
    return {lhs.n + rhs.n};
}
 
int main()
{
    Number<int> i1 = {1}, i2 = {2};
    Number<double> d1 = {2.3}, d2 = {3.5};
    std::cout << "i1i2: " << (i1 + i2).n << "\ni1d2: " << (i1 + d2).n << '\n'
              << "d1i2: " << (d1 + i2).n << "\nd1d2: " << (d1 + d2).n << '\n';
}

Output:

i1i2: 3
i1d2: 4.5
d1i2: 4.3
d1d2: 5.8