Re^3: Does there exist a CPAN module for lazily initialized variables?


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Re^3: Does there exist a CPAN module for lazily initialized variables?

by dragonchild (Archbishop)

on Jul 14, 2004 at 19:15 UTC ( [id://374402]=note: print w/replies, xml )

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in reply to Re^2: Does there exist a CPAN module for lazily initialized variables?
in thread Does there exist a CPAN module for lazily initialized variables?

sub build_lazy
{
    my ($var, $callback, @params) = @_;

    
    eval <<__EVAL__;
{
    my \$$var;
    sub $var {
        \\\$var = $callback->(@params) unless defined \$$var;
        \$$var;
    };
}
__EVAL__
}

# Later ...

build_lazy( 'dbh', \&build_dbh, @dbh_params );
build_lazy( 'foo', \&build_foo );
[download]

Of course, you might want some dwimmery for hashes vs. arrays vs. scalars, unless you're ok with everything as a reference. I would be, but that's just me. And, you might want to throw BEGIN or CHECK around the calls to build_lazy(), but that's probably overkill.

------
We are the carpenters and bricklayers of the Information Age.

Then there are Damian modules.... *sigh* ... that's not about being less-lazy -- that's about being on some really good drugs -- you know, there is no spoon. - flyingmoose

I shouldn't have to say this, but any code, unless otherwise stated, is untested

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Re^4: Does there exist a CPAN module for lazily initialized variables?
by jryan (Vicar) on Jul 14, 2004 at 19:27 UTC

Well, if we're going with the sub approach, the eval isn't needed:

use strict;
sub build_lazy {
    my ($name, $callback, @params) = @_;
    
    my $var;
    no strict 'refs';
    *$name = sub {
        $var = $callback->(@params) unless defined $var;
        $var;
    };
}

build_lazy( 'dbh', sub { print @_ }, 'hi');
print dbh(), dbh(); # hi11
[download]

Its not that I don't like this approach (its still a hell of a lot better than what I have now), I just feel that... I don't know, just that its not the be can be done. Then again, I guess I have a weird mental condition where I'm unsatisfied with my code unless it takes on *exactly* the form thats in my mind, and I become uncomfortable when it isn't. I'm kind of weird. Thanks for the idea though.

[reply]
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