use, require and/or blocking for performance?

System

Does it make a difference in terms of performance in Perl whether I use "use" or "require"? It seems like when I use "use" it parses the module regardless of whether I actually use the module or not; I am not sure if it would be the same with require (or what the difference is here really).

Also if I put a use in a conditional, does it not parse the module unless the condition is true? For instance

if ( something )
{
use module;
}

Does module get parsed even if something is not true?

james1

Please see:

http://perldoc.com/perl5.005_03/pod/func/require.html
http://perldoc.com/perl5.005_03/pod/func/use.html
http://perldoc.com/perl5.005_03/pod/perlmod.html

I think the answers to your questions are:

> It seems like when I use "use" it parses the module
> regardless of whether I actually use the module or not; I am
> not sure if it would be the same with require (or what the
> difference is here really).

Both cause the file to be parsed. use additionally imports the module's symbols into the current namespace and is done at compilation time.

> Also if I put a use in a conditional, does it not parse the
> module unless the condition is true?

No, a use statement is always evaluated at compile time. (I think.)

> Does module get parsed even if something is not true?

I think you want to use require, which can be evaluated conditionally. (I think.)

-- James

--
James H Koh
Interwoven Engineering