Re: how to make local variable retain value

[Chas Owens]

On Tue, 2002-04-16 at 14:01, richard noel fell wrote:
> If in a subroutine, I have a statements
> 
> sub
> {
> 
> my $local_var=1
> ....
> 
> 
> $local_var=$local_var+1;
> ....
> 
> }
> then the next time I run this subroutine, $local_var is reinitialized to
> 1. However, I would like to have it retain its value from the previous
> call to the subroutine. For example, if $local_var is 5 at the end of
> the subroutine call, then it would have this initial value the next time
> the subroutine is called. This can be done by making $local_var a global
> variable which I do not want to do. Is there a way to achieve what I am
> trying to do and still retain $local_var as a local variable, sort of
> what is called a static variable in C, I think?
> 
> Thanks,
> Dick Fell

You can declare a my variable that doesn't get redefined like this.

sub has_a_static_var {
        #declare a "static" variable
        my $static if 0;

        if (defined $static) { $static++   }
        else                 { $static = 0 }

        #do stuff
}

N.B. this is bad juju.  You might consider using an our variable
instead, the downside to that is namespace conflicts.  If you define
another our variable with the same name they point to the same variable;
this is a feature (it is the main difference between our and my).

example

sub has_an_our_var {
        our $static;

        if (defined $static) { $static++   }
        else                 { $static = 0 }

        print "\$static in has_an_our_var = $static\n";
}

The problem occurs when you write another function like this

sub has_another_our_var {
        our $static;
        
        if (defined $static) { $static++   }
        else                 { $static = 0 }

        print "\$static in has_another_our_var = $static\n";
}

then these function calls

has_an_our_var();
has_another_our_var();

would print

$static in has_an_our_var = 1
$static in has_another_our_var = 2

The third option is to use a closure, and there is already a good
example of that in another reply.

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