20 General utilities library [utilities] (original) (raw)
20.14.17.1 General [func.wrap.general]
Subclause [func.wrap] describes a polymorphic wrapper class that encapsulates arbitrary callable objects.
20.14.17.2 Class bad_function_call [func.wrap.badcall]
An exception of type bad_function_call is thrown byfunction::operator() ([func.wrap.func.inv]) when the function wrapper object has no target.
namespace std { class bad_function_call : public exception { public: const char* what() const noexcept override;};}
const char* what() const noexcept override;
Returns: Animplementation-defined ntbs.
20.14.17.3 Class template function [func.wrap.func]
20.14.17.3.1 General [func.wrap.func.general]
namespace std { template<class> class function; template<class R, class... ArgTypes> class function<R(ArgTypes...)> { public: using result_type = R; function() noexcept; function(nullptr_t) noexcept; function(const function&); function(function&&) noexcept;template<class F> function(F); function& operator=(const function&); function& operator=(function&&); function& operator=(nullptr_t) noexcept;template<class F> function& operator=(F&&);template<class F> function& operator=(reference_wrapper<F>) noexcept;~function();void swap(function&) noexcept;explicit operator bool() const noexcept; R operator()(ArgTypes...) const;const type_info& target_type() const noexcept;template<class T> T* target() noexcept;template<class T> const T* target() const noexcept;};template<class R, class... ArgTypes> function(R(*)(ArgTypes...)) -> function<R(ArgTypes...)>;template<class F> function(F) -> function<_see below_>;template<class R, class... ArgTypes> bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;template<class R, class... ArgTypes> void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;}
The function class template provides polymorphic wrappers that generalize the notion of a function pointer.
Wrappers can store, copy, and call arbitrary callable objects, given acall signature, allowing functions to be first-class objects.
[Note 1:
The types deduced by the deduction guides for functionmight change in future revisions of C++.
— _end note_]
20.14.17.3.2 Constructors and destructor [func.wrap.func.con]
function(nullptr_t) noexcept;
function(const function& f);
Postconditions: !*this if !f; otherwise,*this targets a copy of f.target().
Throws: Nothing if f's target is a specialization of reference_wrapper or a function pointer.
Otherwise, may throw bad_allocor any exception thrown by the copy constructor of the stored callable object.
Recommended practice: Implementations should avoid the use of dynamically allocated memory for small callable objects, for example, wheref's target is an object holding only a pointer or reference to an object and a member function pointer.
function(function&& f) noexcept;
Postconditions: If !f, *this has no target; otherwise, the target of *this is equivalent to the target of f before the construction, andf is in a valid state with an unspecified value.
Recommended practice: Implementations should avoid the use of dynamically allocated memory for small callable objects, for example, where f's target is an object holding only a pointer or reference to an object and a member function pointer.
template<class F> function(F f);
Constraints: F is Lvalue-Callable ([func.wrap.func]) for argument typesArgTypes... and return type R.
Preconditions: F meets the Cpp17CopyConstructible requirements.
Postconditions: !*this if any of the following hold:
- f is a null function pointer value.
- f is a null member pointer value.
- F is an instance of the function class template, and!f.
Otherwise, *this targets a copy of finitialized with std::move(f).
Throws: Nothing if f is a specialization of reference_wrapper or a function pointer.
Otherwise, may throw bad_allocor any exception thrown by F's copy or move constructor.
Recommended practice: Implementations should avoid the use of dynamically allocated memory for small callable objects, for example, where f is an object holding only a pointer or reference to an object and a member function pointer.
template<class F> function(F) -> function<_see below_>;
Constraints: &F::operator() is well-formed when treated as an unevaluated operand anddecltype(&F::operator()) is of the formR(G::*)(A...) cv & noexceptfor a class type G.
Remarks: The deduced type is function<R(A...)>.
[Example 1: void f() { int i{5}; function g = [&](double) { return i; }; } — _end example_]
function& operator=(const function& f);
Effects: As if by function(f).swap(*this);
function& operator=(function&& f);
Effects: Replaces the target of *thiswith the target of f.
function& operator=(nullptr_t) noexcept;
Effects: If *this != nullptr, destroys the target of this.
Postconditions: !(*this).
template<class F> function& operator=(F&& f);
Constraints: decay_t<F> is Lvalue-Callable ([func.wrap.func]) for argument types ArgTypes... and return type R.
Effects: As if by: function(std::forward<F>(f)).swap(*this);
template<class F> function& operator=(reference_wrapper<F> f) noexcept;
Effects: As if by: function(f).swap(*this);
Effects: If *this != nullptr, destroys the target of this.
20.14.17.3.3 Modifiers [func.wrap.func.mod]
void swap(function& other) noexcept;
Effects: Interchanges the targets of *this and other.
20.14.17.3.4 Capacity [func.wrap.func.cap]
explicit operator bool() const noexcept;
Returns: true if *this has a target, otherwise false.
20.14.17.3.5 Invocation [func.wrap.func.inv]
R operator()(ArgTypes... args) const;
Throws: bad_function_call if !*this; otherwise, any exception thrown by the wrapped callable object.
20.14.17.3.6 Target access [func.wrap.func.targ]
const type_info& target_type() const noexcept;
Returns: If *this has a target of type T,typeid(T); otherwise, typeid(void).
template<class T> T* target() noexcept;template<class T> const T* target() const noexcept;
Returns: If target_type() == typeid(T)a pointer to the stored function target; otherwise a null pointer.
20.14.17.3.7 Null pointer comparison operator functions [func.wrap.func.nullptr]
template<class R, class... ArgTypes> bool operator==(const function<R(ArgTypes...)>& f, nullptr_t) noexcept;
20.14.17.3.8 Specialized algorithms [func.wrap.func.alg]
template<class R, class... ArgTypes> void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>& f2) noexcept;
Effects: As if by: f1.swap(f2);