Re: Am I justified to use a global variable if it must be used in all scopes?

On Sun, May 27, 2012 at 2:33 PM, Phil Stone <[e-mail]> wrote:
> In a program I'm making, I have a variable (which stores an instance of
> a class) that is declared outside of any functions or classes. However,
> I need to be able to call its methods from various class and function
> scopes, and nothing but a global variable would let me do that. This
> variable is simply what the program is centered around, and must be
> accessed and edited by various classes. I'm not sure why a global
> variable would be such a bad habit in this case, especially since it is
> only one.
>
> Can I justify using it?

There are circumstances where it is reasonable, see the other replies.
 However, there's an alternative: define a class which encapsulates
all the processing which needs to be done in your script and make the
Heap a member of this class.  Advantage: you don't have global state
and can instantiate the Processor and have all sorts of methods access
the Heap member. If you change your program to do multiple
calculations in parallel you simply instantiate a Processor for each
Thread and need not fear mixing up state of each individual
processing.

In my experience it is extremely rare that I needed global variables -
so rare I can't actually remember the last time I introduced a global
variable myself.  If at all I use pre defined globals like $stderr and
the like.

Kind regards

robert


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