Re: Confused about a thread-safe singleton example.

From:

"jason.cipriani@gmail.com" <jason.cipriani@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 3 Dec 2008 09:12:47 -0800 (PST)

Message-ID:

<b1606f1f-3bd1-459d-87c3-ca4ff24f88d2@v38g2000yqb.googlegroups.com>

On Dec 3, 3:22 am, anon <a...@no.invalid> wrote:

jason.cipri...@gmail.com wrote:

On Dec 3, 1:47 am, Alan Johnson <aw...@yahoo.com> wrote:

[lots of cutting]

1. Don't use singletons. Ever. Pretty much all of the value of t=

he GoF

Design Patterns book is negated by the fact that they chose to
legitimize Singleton as a design pattern. Singleton is just a fancy
name for global variable. We should call it the Global Variable
(anti)Pattern.

greatly simplifies a lot of application code. And you are correct, in
this case it basically is, in fact, a global variable.

Both of you are not correct. The singleton is not a global variable.

TheClass* instance = NULL;
TheClass * GetInstance()
{
   if ( NULL == instance )
   {
     instance = new TheClass;
   }
   return instance;

}

In this case, the instance is created when the function GetInstance()
gets called the first time, while global variables gets created before
entering main()

Juts to pick nits, in my particular situation I'm instantiating the
object at global scope, so it is initialized before main(), not on
first demand:

static TheClass *instance = new TheClass();

TheClass * GetInstance () {
return instance;
}

Jason