/ 
mem-v0.4.0
River stage one • 3 direct dependents • 6 total dependents
/ mem

NAME

  • mem - use "in-mem" pkgs & force definitions into mem early

VERSION

    Version "0.4.0"

SYNOPSIS

use mem;
use mem(@COMPILE_TIME_DEFINES=qw(a b c));

mem is a trivial pragma to either allow defining the module it is included from as being defined so that later classes or packages in the same file can use the package to pull in a reference to it, or to be able to call its import routine from a different package in the same file.

With parameter assignments or other actions, it forces those assignments to be done, immediately, at compile time instead of later at run time. It can be use, for example, with Exporter, to export typed-sub's among other usages.

EXAMPLE

Following, is a sample program, showing two uses of mem.

use strict; use warnings;

{ package Ar_Type;
    #
    use mem;                                    #1st usage 
    our (@EXPORT, @ISA);
    sub ARRAY (;*) {
        my $p = $_[0]; my $t="ARRAY";
        return @_ ? (ref $p && (1+index($p, $t))) : $t;
    }
    #
    use mem(                                    #2nd usage 
        @EXPORT=qw(ARRAY), @ISA=qw(Exporter)
    #
    )                                           #(also) 2nd usage 
    ;
    use Exporter;
}

package main;
use Ar_Type;
use P;

my @a=(1,2,3);
my ($ed, $light);
    (@$ed, @$light) = (@a, @a);  #ed & light point to copies of @a
bless $ed, "bee";

P "\@a = ref of array" if ARRAY \@a;
P "ref of ed is %s", ref $ed;
P "ed still points to underlying type, 'array'" if ARRAY $ed;
P "Is ref \$light, ARRAY?: %s", (ref $light eq ARRAY) ? 'yes':'no';
P "Does \"ref \$ed\" eq ARRAY?: %s", (ref $ed eq ARRAY) ? 'yes':'no';
P "%s", "#  (Because \"ref \$ed\" is really a bless \"ed\" bee)"
First, the correct output:
@a = ref of array
ref of ed is bee
ed still points to underlying type, 'array'
Is ref $light, ARRAY?: yes
Does ref $ed eq ARRAY?: no
#  (Because ref "ed" is really a bless "ed" bee)
Second, without the first "use mem", presuming the line was commented out:
Can't locate Ar_Type.pm in @INC (@INC contains: 
  /usr/lib/perl5/5.16.2 ...   /usr/lib/perl5/site_perl .) 
  at /tmp/ex line 18.
BEGIN failed--compilation aborted at /tmp/ex line 18.
and, Third, instead of dropping the 1st "use mem;", you drop (or comment out) the 2nd usage in the above example, you get:
Bareword "ARRAY" not allowed while "strict subs" 
  in use at /tmp/ex line 27.
syntax error at /tmp/ex line 27, near "ARRAY \"
Bareword "ARRAY" not allowed while "strict subs" 
  in use at /tmp/ex line 30.
Bareword "ARRAY" not allowed while "strict subs" 
  in use at /tmp/ex line 31.
Execution of /tmp/ex aborted due to compilation errors.

COMMENTS

The first usage allows 'main' to find package Ar_Type, already in memory rather than forcing a library search for it. By default perl doesn't recognize modules already defined in the same file.

The second usage allows the function prototype and definition of 'ARRAY' to be exported in time for use in 'main'. Without it, You could still call ARRAY, but would have to use an ambersand or parens after the subroutine name. By forcing ISA and EXPORT to be defined before Exporter is called, Exporter can export the symbols in time for main AND their prototypes.

Similar or related function(s):

Note: