First off, your second option doesn't compile.

As for the difference between the first and the third, you need to seriously look at maintenance for the answer. For all the code in a given file, you can do a search for "sub foo" and find out what foo does. But, if it's a subroutine from another module, you can't easily find it. If there's just one Mycommonroutines, then you know where it is. But, what if there are 2? 5? 10? It gets a little hairier.

It is for this reason that I and other CPAN authors have started using the following meme: 

# Explicitly state nothing will be imported
use Scalar::Util ();

# Call the function with the complete name
Scalar::Util::weaken( $some_ref );

[download]

For functions like weaken(), this may seem like overkill. But, this kind of habit will help maintainers because it becomes a flag to say "I didn't write this code in this file and this is where you can find it." And, conversely, if it doesn't have a prepended location, then it must be in this file somewhere. Any kind of hint like that will help your maintainer. Remember - code as if the guy who sees you code after you knows where you live and likes to swing axes.

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re^3: Questions about sharing code by dragonchild
in thread Questions about sharing code by bradcathey

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


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.