in reply to looping over constant data structure references

Constants using the constant pragma need not be scalars, they can be arrays lists too: 
use Data::Dumper;
use constant MSG_DATA => { foo => 1 },
                         { bar => 2 },
                         { baz => 3 };

for my $msg (MSG_DATA) {
    print Dumper $msg;
}

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Use [ MSG_DATA ] elsewhere in the code if you need to use the list as an reference.

Incidentally, this feature is the source of many accidental bugs with constant: 

use constant FOO => "xyz",
             BAR => "def",
             BAZ => "abc";

# FOO returns qw/xyz BAR def BAZ abc/
# BAR and BAZ aren't defined as constants

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The programmer probably meant to declare three constants, not one: 
use constant { FOO => "xyz",
               BAR => "def",
               BAZ => "abc" };

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blokhead

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Re: Re: looping over constant data structure references
by leriksen (Curate) on Nov 11, 2003 at 05:09 UTC
    thanks , I'll ponder on that one - it does seem better - a list matches the constant idea better - contents of constant references are mutable, so removing the []'s removes that level of writable-ness, if that's the right term.

    I'd worry about the [MSG_DATA] though - this copies MSG_DATA and returns a reference to the copy - this may or may not be what you want.
    +++++++++++++++++
    #!/usr/bin/perl
use warnings;
use strict;
use brain;

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