# compose()
[Adaptors]

sigc::compose() combines two or three arbitrary functors. More...

## Classes
struct | sigc::compose1_functor< T_setter, T_getter >
| Adaptor that combines two functors. More...
struct | sigc::compose2_functor< T_setter, T_getter1, T_getter2 >
| Adaptor that combines three functors. More...
## Functions
template<class T_action , class T_setter , class T_getter >
void | sigc::visit_each (const T_action& _A_action, const compose1_functor< T_setter, T_getter >& _A_target)
| Performs a functor on each of the targets of a functor.
template<class T_action , class T_setter , class T_getter1 , class T_getter2 >
void | sigc::visit_each (const T_action& _A_action, const compose2_functor< T_setter, T_getter1, T_getter2 >& _A_target)
| Performs a functor on each of the targets of a functor.
template<class T_setter , class T_getter >
compose1_functor< T_setter, T_getter > | sigc::compose (const T_setter& _A_setter, const T_getter& _A_getter)
| Creates an adaptor of type sigc::compose1_functor which combines two functors.
template<class T_setter , class T_getter1 , class T_getter2 >
compose2_functor< T_setter, T_getter1, T_getter2 > | sigc::compose (const T_setter& _A_setter, const T_getter1& _A_getter1, const T_getter2& _A_getter2)
| Creates an adaptor of type sigc::compose2_functor which combines three functors.

## Detailed Description

sigc::compose() combines two or three arbitrary functors.

On invokation parameters are passed on to one or two getter functor(s). The return value(s) are then passed on to the setter function.

Examples:

       float square_root(float a) { return sqrtf(a); }
         float sum(float a, float b) { return a+b; }
         std::cout << sigc::compose(&square_root, &sum)(9, 16); // calls square_root(sum(3,6))
         std::cout << sigc::compose(&sum, &square_root, &square_root)(9); // calls sum(square_root(9), square_root(9))

The functor sigc::compose() returns can be passed into sigc::signal::connect() directly.

Example:

       sigc::signal<float,float,float> some_signal;
         some_signal.connect(sigc::compose(&square_root, &sum));

For a more powerful version of this functionality see the lambda library adaptor sigc::group() which can bind, hide and reorder arguments arbitrarily. Although sigc::group() is more flexible, sigc::bind() provides a means of binding parameters when then total number of parameters called is variable.

## Function Documentation

template <class T_setter , class T_getter1 , class T_getter2 >

compose2_functor<T_setter, T_getter1, T_getter2> sigc::compose | ( | const T_setter & | _A_setter,
|  | const T_getter1 & | _A_getter1,
|  | const T_getter2 & | _A_getter2 |
| ) |  |  | `[inline]`

Creates an adaptor of type sigc::compose2_functor which combines three functors.

Parameters:

  | _A_setter | Functor that receives the return values of the invokation of _A_getter1 and _A_getter2.
  | _A_getter1 | Functor to invoke from operator()().
  | _A_getter2 | Functor to invoke from operator()().

Returns:
  Adaptor that executes _A_setter with the values return from invokation of _A_getter1 and _A_getter2.

template <class T_setter , class T_getter >

compose1_functor<T_setter, T_getter> sigc::compose | ( | const T_setter & | _A_setter,
|  | const T_getter & | _A_getter |
| ) |  |  | `[inline]`

Creates an adaptor of type sigc::compose1_functor which combines two functors.

Parameters:

  | _A_setter | Functor that receives the return value of the invokation of _A_getter.
  | _A_getter | Functor to invoke from operator()().

Returns:
  Adaptor that executes _A_setter with the value returned from invokation of _A_getter.

template <class T_action , class T_setter , class T_getter1 , class T_getter2 >

void sigc::visit_each | ( | const T_action & | _A_action,
|  | const compose2_functor< T_setter, T_getter1, T_getter2 > & | _A_target |
| ) |  |  | `[inline]`

Performs a functor on each of the targets of a functor.

The function overload for sigc::compose2_functor performs a functor on the functors stored in the sigc::compose2_functor object.

template <class T_action , class T_setter , class T_getter >

void sigc::visit_each | ( | const T_action & | _A_action,
|  | const compose1_functor< T_setter, T_getter > & | _A_target |
| ) |  |  | `[inline]`

Performs a functor on each of the targets of a functor.

The function overload for sigc::compose1_functor performs a functor on the functors stored in the sigc::compose1_functor object.