Background : I am refactoring some modules, one of which pulls in a configuration file at compile time. That is, clients of this module use it thus

...
use Config qw(getConfig);
...
my $foo = getConfig('bar');
...
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In Config.pm, the code was originally like this

package Config;

my $initialised = 0;

sub _initialise {
    return if $initialised;
    ... # read config file
    $initialised++;
}

_initialise();

sub getConfig{...}
...
1;
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This worked, but I changed the $initialised from a my to an our so that there was a way to reload a config file if required (I've changed this to a Reload() method now)

And because I wanted to make clearer that the call to _initialise() was a deliberate decision, I put it in a BEGIN {} block - to me it stands out a lot clearer that the bare statement in the original.

So we have

package Config;

our $initialised = 0;

sub _initialise {
    ... # as before
}

BEGIN {
    _initialise();
}
...
1;
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Now because I like writing correct code, I wrapped all this in a test harness ala Test::More, and took advantage of the fact that $initialised was a package global to write a test like

...
use_ok('Config');
is($Config::initialised, 1); # initialisation completed OK
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And guess what, I got

t/Config....Name "Config::var" used only once: possible typo at t/Conf
+ig.t line 9.
#     Failed test (t/Config.t at line 9)
#          got: '0'
#     expected: '1'
# Looks like you failed 1 tests of 2.
t/Config....dubious
        Test returned status 1 (wstat 256, 0x100)
DIED. FAILED test 2
        Failed 1/2 tests, 50.00% okay
Failed Test Stat Wstat Total Fail  Failed  List of Failed
----------------------------------------------------------------------
+---------
t/Config.t     1   256     2    1  50.00%  2
Failed 1/1 test scripts, 0.00% okay. 1/2 subtests failed, 50.00% okay.
make: *** [test_dynamic] Error 2
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It looks like the initialisation never happened - but I know it happened because I sprinkled a lot of print's in _initialise() to see it working. So it looks like the our $initialised = 0; is clobbering the value set in the BEGIN, at run time. I hope I'm not using the terms compile/run time too loosely.

After pondering and playing for a while, I came up with this version that seems to be correct.

package Config;

sub _initialise {
    ... # as before
}

BEGIN {
    our $initialised = 0;

    _initialise();
}

1;
[download]

This works correctly (though I still get the warning about the var only used once), but the declaration of the our $initialised in the BEGIN looks weird. I suppose if you think about the BEGIN as getting run-time behaviour at compile time, it looks less weird, if you squint.