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Posted 14 Oct 2011

Removing Ugly Flags in C++

, 18 Oct 2011
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Using the Call Gate idiom to reduce number of boolean flags and state variables.
Let's consider a typical use case.

struct car
{
  car()
    :started_(false)
  {
  }
  ~car()
  {
    stop();
  }
 
  void start()
  {
    if(started_)
       return;
    do_start();
    started_=true;
  }
  void stop()
  {
    if(!started_)
       return;
    do_stop();
    started_=false;
  }
private:
  bool started_;
 
  // do actual work
  void do_start();
  void do_stop();
};

Doesn't the 'started_' flag look ugly? It does to me. With the Call Gate idiom, that could be changed to:

struct car
{
  car()
    :start_( boost::bind(&car::do_play, get_this()) )
    ,stop_( boost::bind(&car::do_stop, get_this()) )
  {
    //wire the gates
    start_.wire_on(stop_); //'start' opens the 'stop' gate
    stop_.wire_on(start_); //'stop' opens the 'start' gate
  }
  ~car()
  {
    stop();
  }
 
  void start()
  {
    start_();
  }
  void stop()
  {
    stop_();
  }
 
private:
  gate start_;
  gate stop_;
 
  car* get_this() { return this; }
 
  // do actual work
  void do_start();
  void do_stop();
};


Replacing only one bool with call gates is probably an overkill, but there is a more interesting sample in Call Gate Idiom, and an actual implementation of the call gates.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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egladysh
United States United States
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Comments and Discussions

 
GeneralReason for my vote of 2 What looks ugly to me in the first p... Pin
nv314-Dec-11 4:16
membernv314-Dec-11 4:16 
GeneralMy vote of 5: It is a nice way to hide the annoying state ca... Pin
semmel7125-Oct-11 2:06
membersemmel7125-Oct-11 2:06 
GeneralReason for my vote of 5 Nice! It centralizes the setup of th... Pin
semmel7125-Oct-11 2:02
membersemmel7125-Oct-11 2:02 
GeneralReason for my vote of 1 Why make it simple when you can make... Pin
YvesDaoust24-Oct-11 23:01
memberYvesDaoust24-Oct-11 23:01 
GeneralReason for my vote of 3 Replacing ugly Code with bloated ugl... Pin
Johann Anhofer24-Oct-11 10:01
memberJohann Anhofer24-Oct-11 10:01 
GeneralReason for my vote of 1 The article is way too short to expl... Pin
Wolfgang_Baron18-Oct-11 13:18
memberWolfgang_Baron18-Oct-11 13:18 
GeneralFor a more complex example, please see the player type at th... Pin
egladysh18-Oct-11 7:06
memberegladysh18-Oct-11 7:06 
GeneralReason for my vote of 2 No practical application comes easil... Pin
xelous218-Oct-11 3:29
memberxelous218-Oct-11 3:29 
GeneralReason for my vote of 4 Interesting subject, would love to s... Pin
Julien Villers17-Oct-11 22:32
memberJulien Villers17-Oct-11 22:32 
GeneralReason for my vote of 4 An interesting idiom. Pin
Jon Summers17-Oct-11 9:33
memberJon Summers17-Oct-11 9:33 
QuestionWhy replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang18-Oct-11 3:54
memberStefan_Lang18-Oct-11 3:54 
AnswerRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh18-Oct-11 7:40
memberegladysh18-Oct-11 7:40 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang18-Oct-11 23:26
memberStefan_Lang18-Oct-11 23:26 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
xelous219-Oct-11 0:12
memberxelous219-Oct-11 0:12 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh19-Oct-11 7:54
memberegladysh19-Oct-11 7:54 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang19-Oct-11 22:49
memberStefan_Lang19-Oct-11 22:49 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh20-Oct-11 6:50
memberegladysh20-Oct-11 6:50 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang21-Oct-11 0:40
memberStefan_Lang21-Oct-11 0:40 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh21-Oct-11 6:38
memberegladysh21-Oct-11 6:38 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang25-Oct-11 4:59
memberStefan_Lang25-Oct-11 4:59 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh25-Oct-11 5:41
memberegladysh25-Oct-11 5:41 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
Stefan_Lang25-Oct-11 5:58
memberStefan_Lang25-Oct-11 5:58 
GeneralRe: Why replace an ugly flag with two more ugly objects at the cost of functionality and maintainability? Pin
egladysh25-Oct-11 7:01
memberegladysh25-Oct-11 7:01 
GeneralFeedback Mechanism Absent Pin
xelous218-Oct-11 3:26
memberxelous218-Oct-11 3:26 
GeneralRe: Feedback Mechanism Absent Pin
egladysh18-Oct-11 7:50
memberegladysh18-Oct-11 7:50 
QuestionCouple of criticisms Pin
Don Clugston17-Oct-11 21:34
memberDon Clugston17-Oct-11 21:34 
AnswerRe: Couple of criticisms Pin
egladysh18-Oct-11 7:55
memberegladysh18-Oct-11 7:55 
AnswerRe: Couple of criticisms Pin
egladysh18-Oct-11 14:25
memberegladysh18-Oct-11 14:25 
AnswerDisagree Pin
ryo-oh-ki17-Oct-11 16:33
memberryo-oh-ki17-Oct-11 16:33 

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