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Postings from May 2000
Ian Phillipps wrote: [snip] > Hmm... I've always (well, since perl 5) done this: > *pi = \3.14159; > You can then read $pi, but not alter it. No XS, modules or tying required. > > ~ % perl -we '*pi=\3.14159;print "pi=$pi\n"; $pi+=1; print "pi now $pi\n";' > pi=3.14159 > Modification of a read-only value attempted at -e line 1. > > I just did a Benchmark and the speed of reading is identical with a > "normal" global scalar. The above is what my readonly pragma does, except it declares & assigns in one step so instead of the two steps: use vars '$pi' ; *pi = \3.142 ; you can simply: use readonly '$pi' => 3.142 ; and that's it. I'm sure you can guess what the following based on your examples will output... #!/usr/bin/perl -w use strict ; use vars qw( $pi ) ; # I like strict *pi = \3.14159 ; print "$pi\n" ; # Somewhere deep in the same file far far away... *pi = \'splat' ; print "$pi\n" ; The one-liner is the same: # perl -we'*pi=\3.142;print "$pi\n";*pi=\"splat";print "$pi\n"' But the cases that I'm really interested in are where you want to export constants and be sure that they can't be messed up: # File: Try.pm package Try ; use strict ; use vars qw( @ISA @EXPORT $pi ) ; use Exporter() ; @ISA = qw( Exporter ) ; @EXPORT = qw( $pi ) ; *pi = \3.14159; print "Try loaded: $pi\n" ; 1 ; # File: try #!/usr/bin/perl -w use strict ; use vars qw( $pi ) ; use Try ; # Far away... *pi = \'splat' ; # Further away still... print "$pi\n" ; _______________________________________________ Mark Summerfield http://www.perlpress.com