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## Class trackable

boost::signals::trackable — Enables safe use of multicast callbacks.

## Synopsis

    // In header: <boost/signals/trackable.hpp>

    class trackable {
    public:
      // construct/copy/destruct
      trackable();
      trackable(const trackable&);
      trackable& operator=(const trackable&);
      ~trackable();
    };

## Description

The `trackable` class provides automatic disconnection of signals and slots when objects bound in slots (via pointer or reference) are destroyed. The `trackable` class may only be used as a public base class for some other class; when used as such, that class may be bound to function objects used as part of slots. The manner in which a `trackable` object tracks the set of signal-slot connections it is a part of is unspecified.

The actual use of `trackable` is contingent on the presence of appropriate visit_each overloads for any type that may contain pointers or references to trackable objects.

### `trackable` public construct/copy/destruct

1.     trackable();

   Effects: | Sets the list of connected slots to empty.
   Throws: | Will not throw.

2.     trackable(const trackable& other);

   Effects: | Sets the list of connected slots to empty.
   Throws: | Will not throw.
   Rationale: | Signal-slot connections can only be created via calls to an explicit connect method, and therefore cannot be created here when trackable objects are copied.

3.     trackable& operator=(const trackable& other);

   Effects: | Sets the list of connected slots to empty.
   Returns: | `*this`
   Throws: | Will not throw.
   Rationale: | Signal-slot connections can only be created via calls to an explicit connect method, and therefore cannot be created here when trackable objects are copied.

4.     ~trackable();

   Effects: | Disconnects all signal/slot connections that contain a pointer or reference to this trackable object that can be found by visit_each.