[Chicago-talk] More code that will send me to Perl Purgatory

[Steven Lembark]

On Thu, 22 Oct 2009 03:04:03 -0500
Jonathan Rockway <jon-chicagotalk at jrock.us> wrote:

> * On Tue, Oct 20 2009, Dan Rench wrote:
> > At some point JSON.pm renamed its True() to true() and False() to
> > false(). If there was a "deprecated" grace period that supported both
> > it's past. The code I was working on needed to run on a set of servers
> > with up-to-date JSON, as well as one black sheep that's running all
> > ancient libraries on Perl 5.6.1. It couldn't get upgraded for various
> > reasons.
> >
> > I ended up with this (comments removed because it's more fun that way):
> >
> > my $JSON_true = eval { JSON::true() } || eval { JSON::True() };
> > my $JSON_false = eval { JSON::false() };
> >
> > if (! defined $JSON_false) {
> >   $JSON_false = eval { JSON::False() };
> > }
> 
> Uh, "exists" works on the symbol table:
> 
>   use JSON;
>   say 'False' if exists $JSON::{False};
>   say 'false' if exists $JSON::{false};

Sorry for the delayed response.

Minimal installer for a named sub:

    use Symbol qw( qualify_to_ref );

    my $handler = \&JSON::False;

    my $ref     = qualify_to_ref 'false', 'JSON';

    # undef avoids warnings w/strict.

    undef &$ref;

    # assign a ref to a glob => install symbol.

    *$ref   = $handler;

with added sanity check:

    ...

    my $ref     = qualify_to_ref 'false', 'JSON';

    *{ $ref{ CODE ] }       # it's already there
    or                      # or
    *$ref   = $handler;     # put it where belongs.

Given that False may not be defined (i.e., this is the
pre-deprecation code):

    my $src = qualify_to_ref 'JSON::False';

    if( my $handler = *{ $src }{ CODE } )
    {
        my $dst = qualify_to_ref 'JSON::False';

        if( *{ $dst }{ CODE } )
        {
            # already got falsies, maybe need pasties?
        }
        else
        {
            # ok, False exists, false does not: add false.

            *$dst   = $handler;
        }
    }
    else
    {
        # no Falsies here at all.
    }

Symbol makes all of this a helluva lot easier.

-- 
Steven Lembark                                          85-09 90th St.
Workhorse Computing                               Woodhaven, NY, 11421
lembark at wrkhors.com                                    +1 888 359 3508