Pagoda wrote:
> Can I improve the performance of script by using constant?
>
> Which is the better one?
>
> use constant const => 1e-12
>
> or
>
> my $const = 1e-12
>
the current implmentation of constant is that when you say:
use constant const => 1e-12;
it's basically translated into:
sub <caller>::const(){
1e-12;
}
where <caller> is replaced by the caller's package. so for example:
#!/usr/bin/perl -w
use strict;
use constant const => 1e-12;
print const;
__END__
is bascially translated into:
#!/usr/bin/perl -w
use strict;
sub main::const(){
1e-12;
}
print const;
__END__
which when Perl's optimizer comes in, translates it into:
#!/usr/bin/perl -w
use strict;
print 1e-12;
__END__
that's how you achive the constantness of a variable and a bit of
performance increase. it has roughly the same affact as saying:
[panda]# perl -MO=Deparse -e 'sub const(){1e-2} print const'
print 0.01;
-e syntax OK
notice the function disappear. i would recommand that you use constant
whenever possible regardless of whether it really makes your code goes
faster because of the gain of readability.
btw, you statment:
my $const = 1e-21;
is not a const at all. it's just a scalar.
david
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