Lambda functions (desde C++11)
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Constrói uma oclusão: uma função objeto anônima capaz de captar as variáveis no escopo.
[editar] Sintaxe
[ captures ] <tparams>(opcional)(c++20) ( params ) specifiers exception attr -> ret requires(opcional)(c++20) { body }
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[ captures ] ( params ) -> ret { body }
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[ captures ] ( params ) { body }
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[ captures ] { body }
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1) Declaração completa.
2) Declaração de um const lambda: os objetos capturados por cópia são tratados como const no corpo do lambda.
3) Trailing-return-type omitido: o tipo de retorno do functor, operator(), da oclusão é deduzido a partir da declaração do tipo de retorno da mesma forma que uma função quando seu tipo de retorno é declarado auto.
4) Lista de parâmetros omitida: função sem argumentos, como se a lista de parâmetros fosse (). Essa forma apenas pode ser utilizada caso nenhum dos seguintes tipos de retorno forem usados: constexpr, mutable, exception specification, attributes ou trailing return type.
[editar] Explicação
| mutable | - | body permite modificar os parâmetros capturados por cópia, e chamar suas funções não-membro const
Original: allows body to modify the parameters captured by copy, and to call their non-const member functions The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| exception | - | fornece o especificação de exceção ou o noexcept cláusula de operador () do tipo de fecho
Original: provides the especificação de exceção or the noexcept cláusula for operator() of the closure type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| attribute | - | fornece o especificação de atributo de operador () do tipo de fecho
Original: provides the especificação de atributo for operator() of the closure type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. {{par | capture |{{tr| especifica quais símbolos visíveis no âmbito em que a função é declarada será visível no interior do corpo da função. Uma lista de símbolos pode ser passado como se segue:
A list of symbols can be passed as follows:
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| params | - | A lista de parâmetros, como no nomeado funções
Original: The list of parameters, as in nomeado funções The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| ret | - | Tipo de retorno. Se não estiver presente é implícitos nas declarações de função de retorno (ou nulo se não devolver qualquer valor)
Original: Return type. If not present it's implied by the function return statements ( or void if it doesn't return any value) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| body | - | Corpo da função
Original: Function body The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
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ClosureType ::Original:ClosureType::The text has been machine-translated via Google Translate.
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| ret operator()(params) const { body } |
(a palavra-chave mutável não foi utilizado) | |
| ret operator()(params) { body } |
(a palavra-chave foi usada mutável) | |
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::The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.operator ret(*)(params)
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| typedef ret(*F)(params); operator F() const; |
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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::The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.ClosureType()
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| ClosureType() = delete; |
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| ClosureType(const ClosureType& ) = default; |
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| ClosureType(ClosureType&& ) = default; |
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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 construtores and mover construtores.
ClosureType ::Original:ClosureType::The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.operator=()
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| ClosureType& operator=(const ClosureType&) = delete; |
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Closure types are not CopyAssignable.
ClosureType ::Original:ClosureType::The text has been machine-translated via Google Translate.
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| ~ClosureType() = default; |
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The destructor is implicitly-declared.
ClosureType ::Original:ClosureType::The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.CapturedParam
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| T1 a; T2 b; |
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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.
| Esta seção está incompleta Motivo: scope rules, capture list rules, nested lambdas, implicit capture vs odr use, decltype |
[editar] Exemplo
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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'; }
Saída:
c: 5 6 7 func: 10
[editar] Veja também
| auto especificador | especifica um tipo definido por uma (C++11) expressão
Original: specifies a type defined by an expression (C++11) The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. |
| (C++11) |
envolve objeto que pode ser chamado de qualquer tipo com a assinatura especificada função chamada Original: wraps callable object of any type with specified function call signature The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (modelo de classe) |
