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Lambda functions (desde C++11)

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Lenguaje C++
Los temas generales
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General topics
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Control de flujo
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Flow control
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Sentencias condicionales ejecución
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Conditional execution statements
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Instrucciones de iteración
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Iteration statements
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Ir declaraciones
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Jump statements
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Funciones
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Functions
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declaración de la función
lambda declaración de la función
función de plantilla
especificador inline
especificaciones de excepción (obsoleto)
noexcept especificador (C++11)
Excepciones
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Exceptions
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Los espacios de nombres
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Namespaces
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Tipos
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Types
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decltype specifier (C++11)
Los especificadores
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Specifiers
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cv especificadores
almacenamiento duración especificadores
constexpr especificador (C++11)
auto especificador (C++11)
alignas especificador (C++11)
Inicialización
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Initialization
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Los literales
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Literals
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Expresiones
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Expressions
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representaciones alternativas
Utilidades
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Utilities
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Tipos
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Types
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typedef declaration
alias de tipo de declaración (C++11)
atributos (C++11)
Lanza
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Casts
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conversiones implícitas
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-cast estilo y funcional
De asignación de memoria
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Memory allocation
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Clases
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Classes
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Clase propiedades específicas de la función
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Class-specific function properties
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Funciones especiales miembro
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Special member functions
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Plantillas
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Templates
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clase de plantilla
función de plantilla
plantilla de especialización
paquetes de parámetros (C++11)
Varios
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Miscellaneous
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Montaje en línea
 
Construye un cierre: un objeto no identificado función capaz de capturar variables de alcance .
Original:
Constructs a cierre: an unnamed function object capable of capturing variables in scope.
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Contenido

[editar] Sintaxis

[ capture ] ( params ) mutable exception attribute -> ret { body } (1)
[ capture ] ( params ) -> ret { body } (2)
[ capture ] ( params ) { body } (3)
[ capture ] { body } (4)
1)
Declaración completa
Original:
Full declaration
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2)
Declaración de una lambda construcción: los objetos capturados por la copia no se pueden modificar .
Original:
Declaration of a const lambda: the objects captured by copy cannot be modified.
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3)
Omitido trailing-return-type: el tipo de retorno de operator() el cierre se deduce de acuerdo con las siguientes reglas:
Original:
Omitted trailing-return-type: the return type of the closure's operator() is deduced according to the following rules:
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  • si la body consiste en la declaración return único, el tipo de retorno es el tipo de la expresión que se devuelve (después de rvalue-a-valor-i,-matriz de puntero-, o función a puntero conversión implícita)
    Original:
    if the body consists of the single return statement, the return type is the type of the returned expression (after rvalue-to-lvalue, array-to-pointer, or function-to-pointer implicit conversion)
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  • de lo contrario, el tipo de retorno es void
    Original:
    otherwise, the return type is void
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4)
Omitido lista de parámetros: función no toma ningún argumento, como si la lista de parámetros se ()
Original:
Omitted parameter list: function takes no arguments, as if the parameter list was ()
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[editar] Explicación

mutable -
body permite modificar los parámetros capturados por copia, y que llamen a sus no-const funciones miembro
Original:
allows body to modify the parameters captured by copy, and to call their non-const member functions
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exception -
proporciona la salvo especificación o la noexcept cláusula para el operador () del tipo de cierre
Original:
provides the salvo especificación or the noexcept cláusula for operator() of the closure type
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attribute -
proporciona la atributo especificado para el operador () del tipo de cierre
Original:
provides the atributo especificado for operator() of the closure type
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{{par | capture |{{tr| especifica los símbolos visibles en el ámbito en el que se declara la función será visible en el interior del cuerpo de la función. Una lista de símbolos se puede pasar como sigue:

  • [a,&b] donde a es capturado por su valor y b es capturado por referencia.
  • [this] captura la [[cpp / idioma / este| specifies which symbols visible in the scope where the function is declared will be visible inside the function body.

A list of symbols can be passed as follows:

  • [a,&b] where a is captured by value and b is captured by reference.
  • [this] captures the [[cpp/language/this}}|this pointer]]
  • [&] captures all symbols by reference
  • [=] captures all by value
  • [] captures nothing }}
params -
La lista de parámetros, como en de funciones con nombre
Original:
The list of parameters, as in de funciones con nombre
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ret -
Tipo de retorno. Si no está presente lo que está implícito en las declaraciones de función de retorno (o nulo si no devuelve ningún valor)
Original:
Return type. If not present it's implied by the function return statements ( or void if it doesn't return any value)
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body -
Función del cuerpo
Original:
Function body
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La expresión lambda construye un objeto sin nombre temporal de único sin nombre no-unión no-agregado tipo, conocido como' tipo de cierre, que tiene los siguientes miembros:
Original:
The lambda expression constructs an unnamed temporary object of unique unnamed non-union non-aggregate type, known as closure type, which has the following members:
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ClosureType ::
Original:
ClosureType::
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operator()

ret operator()(params) const { body }
(la palabra clave mutable no se utilizó)
ret operator()(params) { body }
(la palabra clave mutable se utilizó)

Executes the body of the lambda-expression, when invoked. When accessing a variable, accesses its captured copy (for the entities captured by copy), or the original object (for the entities captured by reference). Unless the keyword mutable was used in the lamda-expression, the objects that were captured by copy are non-modifiable from inside this operator().

Dangling references

If an entity is captured by reference, implicitly or explicitly, and the function call operator of the closure object is invoked after the entity's lifetime has ended, undefined behavior occurs. The C++ closures do not extend the lifetimes of the captured references.

ClosureType ::
Original:
ClosureType::
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operator ret(*)(params)

typedef ret(*F)(params);
operator F() const;

This member function is only defined if the capture list of the lambda-expression is empty.

The value returned by this conversion function is a function pointer that, when invoked, has the same effect as invoking the closure object's function call operator directly.

ClosureType ::
Original:
ClosureType::
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ClosureType()

ClosureType() = delete;
ClosureType(const ClosureType& ) = default;
ClosureType(ClosureType&& ) = default;

Closure types are not DefaultConstructible. The copy constructor and the move constructor are implicitly-declared and may be implicitly-defined according to the usual rules for implicit copiar constructores and mover constructores.

ClosureType ::
Original:
ClosureType::
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operator=()

ClosureType& operator=(const ClosureType&) = delete;

Closure types are not CopyAssignable.

ClosureType ::
Original:
ClosureType::
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~ClosureType()

~ClosureType() = default;

The destructor is implicitly-declared.

ClosureType ::
Original:
ClosureType::
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CapturedParam

T1 a;

T2 b;

...

If the lambda-expression captures anything by copy (either implicitly with capture clause [=] or explicitly with a capture that does not include the character &, e.g. [a, b, c]), the closure type includes unnamed non-static data members, declared in unspecified order, that hold copies of all entities that were so captured.

The type of each data member is the type of the corresponding captured entity, except if the entity has reference type (in that case, references to functions are captured as-is, and references to objects are captured as copies of the referenced objects).

For the entities that are captured by reference (with the default capture [&] or when using the character &, e.g. [&a, &b, &c]), it is unspecified if additional data members are declared in the closure type.

[editar] Ejemplo

Este ejemplo muestra cómo pasar una lambda a un algoritmo genérico y objetos de la que resulta de una declaración lambda, se pueden almacenar en objetos std::function .
Original:
This example shows how to pass a lambda to a generic algorithm and that objects resulting from a lambda declaration, can be stored in std::function objects.
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#include <vector>
#include <iostream>
#include <algorithm>
#include <functional>
 
int main()
{
    std::vector<int> c { 1,2,3,4,5,6,7 };
    int x = 5;
    c.erase(std::remove_if(c.begin(), c.end(), [x](int n) { return n < x; } ), c.end());
 
    std::cout << "c: ";
    for (auto i: c) {
        std::cout << i << ' ';
    }
    std::cout << '\n';
 
    std::function<int (int)> func = [](int i) { return i+4; };
    std::cout << "func: " << func(6) << '\n'; 
}

Output:

c: 5 6 7
func: 10

[editar] Ver también

auto especificador
especifica un tipo definido por una (C++11) expresión
Original:
specifies a type defined by an expression (C++11)
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[edit]
(C++11)
envuelve objeto que se puede llamar de cualquier tipo con la firma especificada llamada de función
Original:
wraps callable object of any type with specified function call signature
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(clase de plantilla) [edit]