I've just started defining constants with "use constant", and I'm seeing some, er, non-intuitive behavior. :-)

Here is a code snippet and its output: 

use strict;

BEGIN
  {
  use constant     ROTATE => 1; 
  use constant       HOLD => 2; 
  use constant      FLASH => 3; 
  use constant  NUM_MODES => 3;
  # etc...
  }

my %modestring = 
  (
  ROTATE => "a",
    HOLD => "b",
   FLASH => "c",
  # etc...
  );

  my $mode = int(rand NUM_MODES) + 1;
  print "random mode string is ", $modestring{$mode} || "empty", "\n";
+   
  print "string for 1 is ", $modestring{1} || "empty", "\n";   
  print "string for ROTATE is ", $modestring{ROTATE} || "empty", "\n";
+   

random mode string is empty
string for 1 is empty
string for ROTATE is a

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I fixed the problem by using "," instead of "=>" when ititializing the hash, but I don't understand why the code doesn't work as written. Since the constant definitions are in a BEGIN block, shouldn't their values be substituted throughout the source before the hash is initialized?

laughingboy

In reply to Behavior of compile-time constants? by laughingboy

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