Beefy Boxes and Bandwidth Generously Provided by pair Networks
"be consistent"
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
Hi,

I am writing a simple plugin system. I'm not sure whether I'm going to use it, but it's more like a way to explore Perl.

So, I have an array which contains packages names. Those packages should have a sub 'ReceiveMessage'.
A package called Communications contains a sub 'SendMessage'.
This SendMessage loops over the array to check which packages do have a ReceiveMessage and send a message to it. Currently, the array consists of one item: "Communications".

package Communications; sub SendMessage { my $msg = join("", @_); foreach my $cpack (@main::plugpack) { if (defined eval "${cpack}::ReceiveMessage") { eval "\&${cpack}::ReceiveMessage('$msg')"; } } } sub ReceiveMessage { print "Communications::ReceiveMessage('$_[0]')\n"; }
Of course I call the SendMessage sub once: &Communications::SendMessage("Hello, World!");
The strange thing is, I get output like I called SendMessage twice:
Use of uninitialized value in concatenation (.) or string at D:\device +\modem\internet\Xitami\cgi-bin\index.pl line 48. Communications::ReceiveMessage('') Communications::ReceiveMessage('Hello, World!')
It appears to me that ReceiveMessage is not only called when the message is sent, but also when SendMessage checks it's existance. How can I prevent this?

Update: just clarified the last paragraph a little
Update: removed line of code which was coded in a inconsistent style and only was there for debug purposes :)

In reply to See if a certain package has a certain sub, without executing that sub by muba

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!
  • 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, 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, 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.
  • Log In?
    Username:
    Password:

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

    How do I use this? | Other CB clients
    Other Users?
    Others drinking their drinks and smoking their pipes about the Monastery: (13)
    As of 2015-07-06 12:03 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (73 votes), past polls