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    Lambda functions (depuis C++11)

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    C++
     
    Langage C++
    Sujets gnraux
    Contrle de flux
    Instructions conditionnelles
    Instructions d'itration
    Instructions de saut
    Fonctions
    dclaration de fonction
    expression lambda
    fonction gnrique
    spcificateur inline
    spcification d'exception (obsolte)
    spcificateur noexcept (C++11)
    Exceptions
    Espaces de noms
    Types
    spcificateur decltype (C++11)
    Qualificatifs
    qualificatifs const et volatile
    qualificatifs de stockage
    qualificatif constexpr (C++11)
    qualificatif auto (C++11)
    qualificatif alignas (C++11)
    Initialisation
    Littraux
    Expressions
    oprateurs alternatifs
    Utilitaires
    Types
    dclaration typedef
    dclaration d'alias de type (C++11)
    attributs (C++11)
    Jette
    Original:
    Casts
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    conversions implicites
    conversion const_cast
    conversion static_cast
    conversion dynamic_cast
    conversion reinterpret_cast
    conversions style C et style fonction
    Allocation de mmoire
    Classes
    Qualificatifs spcifiques aux membres de classe
    Fonctions membres spciales
    Modles
    classes gnriques
    fonctions gnriques
    spcialisation de modles
    paquets de paramtres (C++11)
    Divers
    Assembleur
     
    Construit une fermeture: un objet fonction anonyme capable de capturer des variables dans la porte.
    Original:
    Constructs a fermeture: an unnamed function object capable of capturing variables in scope.
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    Syntaxe

    [ capture ] ( params ) mutable exception attribute -> ret { body } (1)
    [ capture ] ( params ) -> ret { body } (2)
    [ capture ] ( params ) { body } (3)
    [ capture ] { body } (4)

    1)

    Dclaration complte
    Original:
    Full declaration
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    2)

    Dclaration d'un lambda const: les objets capturs par copie ne peuvent pas tre modifis .
    Original:
    Declaration of a const lambda: the objects captured by copy cannot be modified.
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    3)

    Type de retour omis: le type de retour de la fermeture operator() est dduite d'aprs les rgles suivantes:
    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 le body est compos de la mention return unique, le type de retour est le type de l'expression retourne (aprs conversion implicite rvalue--lvalue, tableau pointeur, ou fonction--pointeur)
      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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    • autrement, le type de retour est void
      Original:
      otherwise, the return type is void
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    4)

    Liste des paramtres omis: la fonction ne prend aucun argument, comme si la liste des paramtres est ()
    Original:
    Omitted parameter list: function takes no arguments, as if the parameter list was ()
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    Explication

    mutable - Permet
    body de modifier les paramtres capturs par copie, et d'appeler leurs fonctions de membre non-const
    Original:
    allows body to modify the parameters captured by copy, and to call their non-const member functions
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    exception -
    fournit la spcification d'exception ou la noexcept clause pour l'oprateur () du type de fermeture
    Original:
    provides the spcification d'exception or the noexcept clause for operator() of the closure type
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    attribute -
    fournit l'oprateur la spcification d'attribut () du type de fermeture
    Original:
    provides the spcification d'attribut for operator() of the closure type
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    capture -
    spcifie les symboles visibles dans le champ o la fonction est dclare sera visible l'intrieur du corps de la fonction.
    Original:
    {{{2}}}
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    Une liste de symboles peut tre adopte comme suit:

    • [a,&b] o a est captur par valeur et b est captur par rfrence.
    • [this] capte le pointeur this
    • [&] captures all symbols by reference
    • [=] captures all by value
    • [] captures nothing
    params -
    La liste des paramtres, comme dans nomme fonctions
    Original:
    The list of parameters, as in nomme fonctions
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    ret -
    Type de retour. S'il n'est pas prsent il est implicite dans les noncs de retour de fonction (ou void si elle ne retourne aucune valeur)
    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 -
    Corps de la fonction
    Original:
    Function body
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    L'expression lambda construit un objet non identifi temporaire unique, anonyme non syndiqu non agrge type, connu sous le nom' type de fermeture, ce qui comprend les membres suivants:
    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()

    <tbody> </tbody>
    ret operator()(params) const { body }
    		 (
    le mot-cl mutable n'a pas t utilis
    Original:
    the keyword mutable was not used
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    )
    ret operator()(params) { body }
    		 (
    le mot-cl mutable a t utilis
    Original:
    the keyword mutable was used
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    )

    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)

    <tbody> </tbody>
    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()

    <tbody> </tbody>
    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 copier des constructeurs and dplacer des constructeurs.

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

    <tbody> </tbody>
    ClosureType& operator=(const ClosureType&) = delete;

    Closure types are not CopyAssignable.

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

    <tbody> </tbody>
    ~ClosureType() = default;

    The destructor is implicitly-declared.

    ClosureType ::
    Original:
    ClosureType::
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    CapturedParam

    <tbody> </tbody>
    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.

    This section is incomplete
    Reason: scope rules, capture list rules, nested lambdas, implicit capture vs odr use, decltype

    Exemple

    Cet exemple montre comment passer un lambda un algorithme gnrique et que les objets rsultant d'une dclaration lambda, peuvent tre stocks dans des objets 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'; 
}

    Rsultat : 

    c: 5 6 7
func: 10

    Voir aussi

    auto spcificateur
    spcifie un type dfini par l'expression (C++11)
    Original:
    specifies a type defined by an expression (C++11)
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    [edit]
    (C++11)
    		 adaptateur gnrique de foncteur
    (classe gnrique) [edit]
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