Re: Using constants as hash keys

Very nice. Thanks for sharing this choroba.

The inevitable little addendum:

#!/usr/bin/env perl

use strict;
use warnings;
use Const::Fast;
use Data::Dump;
use feature qw(say);

const our $A => 12;
const our $B => 13;

print $];
print qx(corelist Const::Fast);

my %hash = (
    $A => 'twelve',
    $B => 'thirteen',
);

dd \%hash;

say $hash{$A};
say $hash{$B};

for ( sort ( keys(%hash) ) ) {
    say qq($_  =>  $hash{$_});
}

__END__

karls-mac-mini:playground karl$ ./constant.pl
5.024001
Data for 2017-01-14
Const::Fast was not in CORE (or so I think)
{ 12 => "twelve", 13 => "thirteen" }
twelve
thirteen
12  =>  twelve
13  =>  thirteen
[download]

Best regards, Karl

ŤThe Crux of the Biscuit is the Apostropheť

perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

Comment on Re: Using constants as hash keys Select or Download Code

Replies are listed 'Best First'.

Re^2: Using constants as hash keys
by Athanasius (Archbishop) on Jan 05, 2018 at 15:10 UTC

Hello karlgoethebier,

I’ve been a fan of Const::Fast since I discovered it recently in the Perl Advent Calendar 2017. But constant does have one important advantage over Const::Fast: it is applied at compile time, whereas Const::Fast takes effect only at run time. So, in this respect, Const::Fast suffers from the same limitation, identified by choroba, as the &CONSTANT syntax for the constant pragma — the constant isn’t inlined:

 0:59 >perl -Mstrict -MData::Dump -MConst::Fast -we "use constant A =>
+ 12; const our $B => 13; my %h = ( (A) => 'twelve', $B => 'thirteen')
+; dd \%h;"
{ 12 => "twelve", 13 => "thirteen" }

 0:59 >perl -Mstrict -MO=Deparse -MData::Dump -MConst::Fast -we "use c
+onstant A => 12; const our $B => 13; my %h = ( (A) => 'twelve', $B =>
+ 'thirteen'); dd \%h;"
BEGIN { $^W = 1; }
use strict;
use Data::Dump;
use Const::Fast;
use constant ('A', 12);
&const(\our $B, 13);
my(%h) = (12, 'twelve', $B, 'thirteen');
dd(\%h);
-e syntax OK

 0:59 >
[download]

(AFAICT, this also makes Const::Fast unsuitable in situations where one wants to write code like this:

use constant DEBUG => 0;
...
perform_some_debugging_operation() if DEBUG;
...
[download]

and have the compiler remove the expensive operation when it sees that DEBUG is false.)

Update: Changed perform_expensive_debugging_operation() to perform_some_debugging_operation(), because, as Eily pointed out in a private message, the cost of the operation is irrelevant if DEBUG (or $DEBUG) is false.

Cheers,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

[reply]
[d/l]
[select]

Re^3: Using constants as hash keys

by karlgoethebier (Abbot) on Jan 05, 2018 at 15:28 UTC

"...the same limitation..."

Yes. Thanks. Unfortunately this is true. And i begin to see it clearly now. Best regards, Karl

ŤThe Crux of the Biscuit is the Apostropheť

perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

[reply]
[d/l]


Come for the quick hacks, stay for the epiphanies.
	PerlMonks