Multiple uses

HairyMonkey has asked for the wisdom of the Perl Monks concerning the following question:

Howdy,
i've looked everywhere but no answers yet...
if in one script i have the lines

use ModuleA;
use ModuleB;
[download]

if in ModuleA i ALSO have the line

use ModuleB;
[download]

(i.e. one module used twice in 2 separate scripts/packages)
what will happen as regards memory usage/resources?
how many times will ModuleB be compiled?
what memory is assigned? 1 block (block ?) or 2 ?

thanks

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Re: Multiple uses by Kanji (Parson) on Mar 27, 2002 at 12:37 UTC
how many times will ModuleB be compiled? Once ... unless you delete it's key/value pair from `%INC`, which Perl uses to determine if it's already loaded a particular module/file. For details, see the "semantics similar to" code example in `perldoc require`, which I've excerpted the appropriate bits of (plus pointer comments) below for convenience. `sub require { my($filename) = @_; return 1 if $INC{$filename}; # <-- already loaded? # ... pull in the module $INC{$filename} = $realfilename; # <-- stop future reloads return $result; }` [download] --k.	[reply] [d/l]
Re: Multiple uses by RMGir (Prior) on Mar 27, 2002 at 12:27 UTC
Simple test: `# ModuleA.pm use ModuleB; BEGIN { print "ModuleA::BEGIN\n"; } 1; # ModuleB.pm BEGIN { print "ModuleB::BEGIN\n"; } 1; # main.pl use ModuleA; use ModuleB; BEGIN { print "main::BEGIN\n"; }` [download] Create those 3 files, then run main.pl. `$ perl main.pl ModuleB::BEGIN ModuleA::BEGIN main::BEGIN` [download] It looks like perl does "the right thing". -- Mike	[reply] [d/l] [select]