Class template functionN

boost::functionN — A set of generalized function pointers that can be used for callbacks or wrapping function objects.

Synopsis

template<typename R, typename T1, typename T2, ..., typename TN, 
         typename Allocator = std::allocator<void> > 
class functionN : public function_base {
public:
  // types
  typedef R         result_type;         
  typedef Allocator allocator_type;      
  typedef T1        argument_type;         // If N == 1
  typedef T1        first_argument_type;   // If N == 2
  typedef T2        second_argument_type;  // If N == 2
  typedef T1        arg1_type;           
  typedef T2        arg2_type;           
     .
     .
     .
  typedef TN        argN_type;           

  // static constants
  static const int arity = N;

  // Lambda library support
  template<typename Args> 
  struct sig {
    // types
    typedef result_type type;
  };

  // construct/copy/destruct
  functionN();
  functionN(const functionN&);
  template<typename F> functionN(F);
  functionN& operator=(const functionN&);
  ~functionN();

  // modifiers
  void swap(const functionN&);
  void clear();

  // capacity
  bool empty() const;
  operator safe_bool() const;
  bool operator!() const;

  // target access
  template<typename Functor> Functor* target();
  template<typename Functor> const Functor* target() const;
  template<typename Functor> bool contains(const Functor&) const;

  // invocation
  result_type operator()(arg1_type, arg2_type, ..., argN_type) const;
};

// specialized algorithms
template<typename T1, typename T2, ..., typename TN, typename Allocator> 
  void swap(functionN<T1, T2, ..., TN, Allocator>&, 
            functionN<T1, T2, ..., TN, Allocator>&);

// comparison operators
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(const functionN<T1, T2, ..., TN, Allocator>&, Functor);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(Functor, const functionN<T1, T2, ..., TN, Allocator>&);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(const functionN<T1, T2, ..., TN, Allocator>&, 
                  reference_wrapper<Functor>);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(reference_wrapper<Functor>, 
                  const functionN<T1, T2, ..., TN, Allocator>&);
template<typename T1, typename T2, ..., typename TN, typename Allocator1, 
         typename U1, typename U2, ..., typename UN, typename Allocator2> 
  void operator==(const functionN<T1, T2, ..., TN, Allocator1>&, 
                  const functionN<U1, U2, ..., UN, Allocator2>&);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(const functionN<T1, T2, ..., TN, Allocator>&, Functor);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(Functor, const functionN<T1, T2, ..., TN, Allocator>&);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(const functionN<T1, T2, ..., TN, Allocator>&, 
                  reference_wrapper<Functor>);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(reference_wrapper<Functor>, 
                  const functionN<T1, T2, ..., TN, Allocator>&);
template<typename T1, typename T2, ..., typename TN, typename Allocator1, 
         typename U1, typename U2, ..., typename UN, typename Allocator2> 
  void operator!=(const functionN<T1, T2, ..., TN, Allocator1>&, 
                  const functionN<U1, U2, ..., UN, Allocator2>&);

Description

Class template functionN is actually a family of related classes function0, function1, etc., up to some implementation-defined maximum. In this context, N refers to the number of parameters.

`functionN` construct/copy/destruct

```
functionN();
```
Postconditions: this->empty()
Throws: Will not throw.
```
functionN(const functionN& f);
```
Postconditions: Contains a copy of the f's target, if it has one, or is empty if f.empty().
Throws: Will not throw unless copying the target of f throws.
```
template<typename F> functionN(F f);
```
Requires: F is a function object Callable from this.
Postconditions: *this targets a copy of f if f is nonempty, or this->empty() if f is empty.
Throws: Will not throw when f is a stateless function object.
```
functionN& operator=(const functionN& f);
```
Postconditions: *this targets a copy of f's target, if it has one, or is empty if f.empty().
Throws: Will not throw when the target of f is a stateless function object or a reference to the function object.
```
~functionN();
```
Effects: If !this->empty(), destroys the target of this.

`functionN` modifiers

```
void swap(const functionN& f);
```
Effects: Interchanges the targets of *this and f.
Throws: Will not throw.
```
void clear();
```
Postconditions: this->empty()
Throws: Will not throw.

`functionN` capacity

```
bool empty() const;
```
Returns: false if this has a target, and true otherwise.
Throws: Will not throw.
```
operator safe_bool() const;
```
Returns: A safe_bool that evaluates false in a boolean context when this->empty(), and true otherwise.
Throws: Will not throw.
```
bool operator!() const;
```
Returns: this->empty()
Throws: Will not throw.

`functionN` target access

```
template<typename Functor> Functor* target();
template<typename Functor> const Functor* target() const;
```
Returns: If this stores a target of type Functor, returns the address of the target. Otherwise, returns the NULL pointer.
Throws: Will not throw.
```
template<typename Functor> bool contains(const Functor& f) const;
```
Returns: true if this->target<Functor>() is non-NULL and function_equal(*(this->target<Functor>()), f)

`functionN` invocation

```
result_type operator()(arg1_type a1, arg2_type a2, ... , argN_type aN) const;
```
Effects: f(a1, a2, ..., aN), where f is the target of *this.
Returns: if R is void, nothing is returned; otherwise, the return value of the call to f is returned.
Throws: bad_function_call if this->empty(). Otherwise, may through any exception thrown by the target function f.

`functionN` specialized algorithms

template<typename T1, typename T2, ..., typename TN, typename Allocator> 
  void swap(functionN<T1, T2, ..., TN, Allocator>& f1, 
            functionN<T1, T2, ..., TN, Allocator>& f2);

Effects: f1.swap(f2)
Throws: Will not throw.

`functionN` comparison operators

template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(const functionN<T1, T2, ..., TN, Allocator>& f, Functor g);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(Functor g, const functionN<T1, T2, ..., TN, Allocator>& f);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(const functionN<T1, T2, ..., TN, Allocator>& f, 
                  reference_wrapper<Functor> g);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator==(reference_wrapper<Functor> g, 
                  const functionN<T1, T2, ..., TN, Allocator>& f);
template<typename T1, typename T2, ..., typename TN, typename Allocator1, 
         typename U1, typename U2, ..., typename UN, typename Allocator2> 
  void operator==(const functionN<T1, T2, ..., TN, Allocator1>& f1, 
                  const functionN<U1, U2, ..., UN, Allocator2>& f2);

Returns: True when f stores an object of type Functor and one of the following conditions applies:

g is of type reference_wrapper<Functor> and f.target<Functor>() == g.get_pointer().
g is not of type reference_wrapper<Functor> and function_equal(*(f.target<Functor>()), g).

Notes: functionN objects are not EqualityComparable.
Rationale: The safe_bool conversion opens a loophole whereby two functionN instances can be compared via ==, although this is not feasible to implement. The undefined

void
        operator==

closes the loophole and ensures a compile-time or link-time error.

template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(const functionN<T1, T2, ..., TN, Allocator>& f, Functor g);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(Functor g, const functionN<T1, T2, ..., TN, Allocator>& f);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(const functionN<T1, T2, ..., TN, Allocator>& f, 
                  reference_wrapper<Functor> g);
template<typename T1, typename T2, ..., typename TN, typename Allocator, 
         typename Functor> 
  bool operator!=(reference_wrapper<Functor> g, 
                  const functionN<T1, T2, ..., TN, Allocator>& f);
template<typename T1, typename T2, ..., typename TN, typename Allocator1, 
         typename U1, typename U2, ..., typename UN, typename Allocator2> 
  void operator!=(const functionN<T1, T2, ..., TN, Allocator1>& f1, 
                  const functionN<U1, U2, ..., UN, Allocator2>& f2);

Returns: True when f does not store an object of type Functor or it stores an object of type Functor and one of the following conditions applies:

g is of type reference_wrapper<Functor> and f.target<Functor>() != g.get_pointer().
g is not of type reference_wrapper<Functor> and !function_equal(*(f.target<Functor>()), g).

Notes: functionN objects are not EqualityComparable.
Rationale: The safe_bool conversion opens a loophole whereby two functionN instances can be compared via !=, although this is not feasible to implement. The undefined

void
        operator!=

closes the loophole and ensures a compile-time or link-time error.