CommandFunctors.h

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//
//  CommandFunctors.h
//  Audacity
//
//  Created by Paul Licameli on 4/22/16.
//
//
 
#ifndef __AUDACITY_COMMAND_FUNCTORS__
#define __AUDACITY_COMMAND_FUNCTORS__
 
class AudacityProject;
class AudacityApp;
class CommandContext;
 
// Forward-declaring this type before including wx/event.h causes strange
// compilation failures with MSVC.
// class wxEvtHandler;
#include <wx/event.h>
 
// Base class for objects, to whose member functions, the CommandManager will
// dispatch.
//
// It, or a subclass of it, must be the first base class of the object, and the
// first base class of that base class, etc., for the same reason that
// wxEvtHandler must be first (that is, the downcast from a pointer to the base
// to a pointer to the object, must be a vacuous operation).
//
// In fact, then, we just make it an alias of wxEvtHandler, in case you really
// need to inherit from wxEvtHandler for other reasons, and otherwise you
// couldn't satisfy the requirement for both base classes at once.
using CommandHandlerObject = wxEvtHandler;
 
// First of two functions registered with each command: an extractor
// of the handler object from the AudacityProject, or null
using CommandHandlerFinder =
   std::function< CommandHandlerObject&(AudacityProject &) >;
 
// Second of two function pointers registered with each command: a pointer
// to a member function of the handler object, or a pointer to a non-member
// function when the CommandHandlerFinder is null
union CommandFunctorPointer {
   using MemberFn =
      void (CommandHandlerObject::*)(const CommandContext &context);
   using NonMemberFn =
      void (*)(const CommandContext &context);
 
   CommandFunctorPointer() = default;
   explicit CommandFunctorPointer(MemberFn memberFn)
      : memberFn{ memberFn } {}
   explicit CommandFunctorPointer(NonMemberFn nonMemberFn)
      : nonMemberFn{ nonMemberFn } {}
 
   MemberFn memberFn;
   NonMemberFn nonMemberFn;
};
 
#endif