# hide(), hide_return()
[Adaptors]

sigc::hide() alters an arbitrary functor in that it adds a parameter whose value is ignored on invocation of the returned functor. More...

## Classes

struct | sigc::hide_functor<-1, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 0, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 1, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 2, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 3, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 4, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 5, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...
struct | sigc::hide_functor< 6, T_functor >
| Adaptor that adds a dummy parameter to the wrapped functor. More...

## Functions

template<class T_functor >
retype_return_functor< void, T_functor > | sigc::hide_return (const T_functor& _A_functor)
| Creates an adaptor of type sigc::retype_return_functor which drops the return value of the passed functor.
template<class T_action , int I_location, class T_functor >
void | sigc::visit_each (const T_action& _A_action, const hide_functor< I_location, T_functor >& _A_target)
| Performs a functor on each of the targets of a functor.
template<int I_location, class T_functor >
hide_functor< I_location, T_functor > | sigc::hide (const T_functor& _A_func)
| Creates an adaptor of type sigc::hide_functor which adds a dummy parameter to the passed functor.

## Detailed Description

sigc::hide() alters an arbitrary functor in that it adds a parameter whose value is ignored on invocation of the returned functor.

Thus you can discard one argument of a signal.

You may optionally specify the zero-based position of the parameter to ignore as a template argument. The default is to ignore the last parameter. (A value of `-1` adds a parameter at the end so sigc::hide<-1>() gives the same result as sigc::hide().)

The type of the parameter can optionally be specified if not deduced.

Examples:

       void foo(int, int);
         // single argument hiding ...
         sigc::hide(&foo)(1,2,3); // adds a dummy parameter at the back and calls foo(1,2)
         sigc::hide<-1>(&foo)(1,2,3); // same as sigc::hide(&foo)(1,2,3) (calls foo(1,2))
         sigc::hide<0>(&foo)(1,2,3); // adds a dummy parameter at the beginning and calls foo(2,3)
         sigc::hide<1>(&foo)(1,2,3); // adds a dummy parameter in the middle and calls foo(1,3)
         sigc::hide<2>(&foo)(1,2,3); // adds a dummy parameter at the back and calls foo(1,2)

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

Example:

       sigc::signal<void,int> some_signal;
         void foo();
         some_signal.connect(sigc::hide(&foo));

sigc::hide() can be nested in order to discard multiple arguments.

Example:

       // multiple argument hiding ...
         sigc::hide(sigc::hide(&foo))(1,2,3,4); // adds two dummy parameters at the back and calls foo(1,2)

sigc::hide_return() alters an arbitrary functor by dropping its return value, thus converting it to a void functor.

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::hide() provides a means of hiding parameters when then total number of parameters called is variable.

## Function Documentation

template <int I_location, class T_functor >

hide_functor<I_location, T_functor> sigc::hide | ( | const T_functor & | _A_func | ) | `[inline]`

Creates an adaptor of type sigc::hide_functor which adds a dummy parameter to the passed functor.

The optional template argument I_location specifies the zero-based position of the dummy parameter in the returned functor (`-1` stands for the last parameter).

Parameters:

  | _A_func | Functor that should be wrapped.

Returns:
  Adaptor that executes _A_func ignoring the value of the dummy parameter.

template <class T_functor >

retype_return_functor<void, T_functor> sigc::hide_return | ( | const T_functor & | _A_functor | ) | `[inline]`

Creates an adaptor of type sigc::retype_return_functor which drops the return value of the passed functor.

Parameters:

  | _A_functor | Functor that should be wrapped.

Returns:
  Adaptor that executes _A_functor dropping its return value.

template <class T_action , int I_location, class T_functor >

void sigc::visit_each | ( | const T_action & | _A_action,
|  | const hide_functor< I_location, T_functor > & | _A_target |
| ) |  |  | `[inline]`

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

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