• Steve Teale (40/40) Oct 16 2011 Is not needed because structs are inherently scope.
• deadalnix (4/44) Oct 17 2011 Nice trick ! However, in D, you have scope(exit) scope(success) and
• travert phare.normalesup.org (Christophe) (32/80) Oct 23 2011 void main(string[] args)

Steve Teale <steve.teale britseyeview.com> writes:

Is not needed because structs are inherently scope.

I'm sure experienced D programmers do this all the time when they want 
something done on exit from a scope, but I never had, and maybe there are 
others who haven't, particularly if coming from a C++ 'use classes for 
everything' background.

import std.stdio;

bool glob;

struct Sentinel
{
   void function() doit;
   bool already;
   this(void function() f)
   {
      doit = f;
      already = false;
   }

   ~this()
   {
      if (!already)
      {
         writeln("Doing it now");
         doit();
      }
      else
         writeln("Won't bother");
   }

   void dontBother() { already = true; }
}

void reset() { glob = false; }

void main(string[] args)
{
   glob = true;
   {
      Sentinel s = Sentinel(&reset);
      writeln("Doing stuff in the scope");
      if (args.length >= 2 && args[1] == "db")
         s.dontBother();
   }
   writeln(glob);
}

deadalnix <deadalnix gmail.com> writes:

Nice trick ! However, in D, you have scope(exit) scope(success) and 
scope(failure) to do similar stuffs.

I personally use both, on a case by case basis.

Le 17/10/2011 06:47, Steve Teale a écrit :
 Is not needed because structs are inherently scope.

 I'm sure experienced D programmers do this all the time when they want
 something done on exit from a scope, but I never had, and maybe there are
 others who haven't, particularly if coming from a C++ 'use classes for
 everything' background.

 import std.stdio;

 bool glob;

 struct Sentinel
 {
     void function() doit;
     bool already;
     this(void function() f)
     {
        doit = f;
        already = false;
     }

     ~this()
     {
        if (!already)
        {
           writeln("Doing it now");
           doit();
        }
        else
           writeln("Won't bother");
     }

     void dontBother() { already = true; }
 }

 void reset() { glob = false; }

 void main(string[] args)
 {
     glob = true;
     {
        Sentinel s = Sentinel(&reset);
        writeln("Doing stuff in the scope");
        if (args.length>= 2&&  args[1] == "db")
           s.dontBother();
     }
     writeln(glob);
 }

travert phare.normalesup.org (Christophe) writes:

Steve Teale , dans le message (digitalmars.D.learn:30117), a écrit :
 Is not needed because structs are inherently scope.
 
 I'm sure experienced D programmers do this all the time when they want 
 something done on exit from a scope, but I never had, and maybe there are 
 others who haven't, particularly if coming from a C++ 'use classes for 
 everything' background.
 
 import std.stdio;
 
 bool glob;
 
 struct Sentinel
 {
    void function() doit;
    bool already;
    this(void function() f)
    {
       doit = f;
       already = false;
    }
 
    ~this()
    {
       if (!already)
       {
          writeln("Doing it now");
          doit();
       }
       else
          writeln("Won't bother");
    }
 
    void dontBother() { already = true; }
 }
 
 void reset() { glob = false; }
 
 void main(string[] args)
 {
    glob = true;
    {
       Sentinel s = Sentinel(&reset);
       writeln("Doing stuff in the scope");
       if (args.length >= 2 && args[1] == "db")
          s.dontBother();
    }
    writeln(glob);
 }



void main(string[] args)
{
  glob = true;
  {
    dontBother=false;
    scope(exit)
    {
      if (!dontBother)
        {
          writeln("Doing it now");
          glob = false;
        }
      else
	{
          writeln("Don't bother");
        }
     }

     writeln("Doing stuff in the scope");
     if (args.length >= 2 && args[1] == "db")
       dontBother() = true;
  }
  writeln(glob);
}


If you're not running a test with a lot of writing, the scope clause is 
just:

scope(exit) if (!dontBother) glob() = false;

The scope exit clause will be run even if you exit via an exception 
(just like the sentinel's dstructor).

As you can see, D as its own syntax to make things when the scope exits, 
so you don't need to build a sentinel struct.
http://d-programming-language.org/exception-safe.html