Beefy Boxes and Bandwidth Generously Provided by pair Networks
more useful options
 
PerlMonks  

comment on

( [id://3333]=superdoc: print w/replies, xml ) Need Help??

Good development techniques usually indicate that one package should exist in one file.

Agreed, but what if I want to use those constants from a subclass, or in some other piece of code? More pre-processor trickery? Ick.

The Perl pragma constants are accessible at runtime, and can be exposed to other modules in a normal Perl fashion.

For those cases where 2+ packages should co-exist in one file, I have often found that I want the same constants for all the packages within a file. But, I have to do things like Parent::SOME_CONSTANT instead of just SOME_CONSTANT, for that specific reason.

One technique you might find applicable is to define a constant and then export it to your other modules, the same way you would if they were spread out over multiple files:

package MyFlags; use constant FooFlag => 42; use constant BarFlag => 23; use base 'Exporter'; BEGIN { @MyFlags::EXPORT_OK = qw( FooFlag BarFlag ); } BEGIN { $::INC{'MyFlags.pm'} ||= __FILE__; } package MyWidgetFactory; use MyFlags qw( FooFlag ); print FooFlag . "\n"; package MyFlyingMonkey; use MyFlags qw( FooFlag BarFlag ); print BarFlag . "\n";

If I want to associate tuber-ness with Potatoes vs. Peaches, I would make it accessible via some method. So, instead of Potato::tuber, I would have Potato->is_tuber, or some such.

Sure, by all means, go ahead and treat it as a method; after all, use constant is mostly just shorthand for making simple subroutines:

package Potato; use constant tuber => 1; package main; print Potato->tuber;

Constant references to hashes/arrays don't seem to have a huge benefit.

Agreed, there's no breakthrough here -- just some syntactic sweetener... If your module's interface features a lot of public methods and only a couple of public package variables, it can be attractive to wrap those references in constant subs.

This is a completely new feature of Perl to me, and one that seems to have huge benefits.

Yup; both the CPP #defines and Perl constants are useful tools, each with their own ups and downs; I hope this post has clarified why, if given the choice, I'd typically use constant.


In reply to Re: Re2: C pre-processor in Perl by simonm
in thread C pre-processor in Perl by dragonchild

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others contemplating the Monastery: (10)
As of 2024-03-28 12:04 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found