in reply to Re^3: Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE ^]/ (updated)
in thread Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE ^]/

darn, constants are not interpolated in strings or regexes.

As I understand it, even with use constant, a constant in Perl is an in line sub. IE: 

use constant PI    => 4 * atan2(1, 1);

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is the short hand for

sub PI
{
    4 * atan2(1, 1);
}

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Which, after compile time constant expression evaluation, simplifies to:

sub PI
{
    3.1415926536; # to the precision available on the machine running 
+the program
}

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which the compiler can then in line where it would otherwise put a sub call.

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Re^5: Unmatched [ in regex; marked by <-- HERE in m/[ <-- HERE ^]/
by LanX (Saint) on Apr 29, 2014 at 17:01 UTC
    > where it would otherwise put a sub call.

    which isn't trivial within strings/regexes.

    the "@{[...]}" trick works but is IMHO a bit oversized for this task.

      DB<109> use constant STR => 1..3

  DB<110> qr/[@{[ STR ]}]/
 => qr/[1 2 3]/

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    thats not interpolation anymore but inline eval.

    Cheers Rolf

    ( addicted to the Perl Programming Language)

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      Here's another way, but I can't say it's any less klutzy. There seems to be no way to avoid the use of some kind of operator for disambiguation. 

      use warnings;
use strict;

use constant STR   => 'a string';
use constant STREF => \'ref to a string';

print qq{one way '${ \STR }' and another '${ +STREF   }' \n};
print qq{and with another disambiguation '${  STREF() }' \n};

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      Output: 

      c:\@Work\Perl\monks>perl constant_interpolation_1.pl
one way 'a string' and another 'ref to a string'
and with another disambiguation 'ref to a string'

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