perl

How to mute that when and given are experimental in Perl?

I am migrating an old toolchain to a new system and now I get plenty of notifications given is experimental or when is experimental. 

$ perl -e 'use v5.10; given (12) { when (12) { print "Hello World" }}'
given is experimental at -e line 1.
when is experimental at -e line 1.
Hello World

I would like my new system to be fully compatible with the old one. By this I mean the exact same output.

Is there a way to mute these notifications without touching the oneliners nor the scripts?

Solution

  • First of all, note that smartmatching will be removed in 5.42.

    To use given+when without warnings, one needs the following:

    # 5.10+
use feature qw( switch );
no if $] >= 5.018, warnings => qw( experimental::smartmatch );

    or

    # 5.18+
use feature qw( switch );
no warnings qw( experimental::smartmatch );

    experimental provides a shortcut for those two statements.

    use experimental qw( switch );

    Finally, you ask how to add this to your programs without changing them (and presumably without changing Perl). That leaves monkeypatching.

    I wouldn't recommend it. It's far easier to write a couple of one-liners to automatically fix up your programs than rewriting Perl's behaviour on the fly.

    But if you want to go in that direction, the simplest solution is probably to write a $SIG{__WARN__} handler that filters out the undesired warnings.

    $SIG{__WARN__} = sub {
   warn($_[0]) if $_[0] !~ /^(?:given|when) is experimental at /;
};

    (Of course, that won't work if your program makes use of $SIG{__WARN__} already.)

    To get it loaded without changing your programs or one-liners, all you have to do is place the patch in a module, and tell Perl to load the module as follows:

    export PERL5OPT=-MMonkey::SilenceSwitchWarning

    $ cat Monkey/SilenceSwitchWarning.pm
package Monkey::SilenceSwitchWarning;

use strict;
use warnings;

$SIG{__WARN__} = sub {
    warn($_[0]) if $_[0] !~ /^(?:given|when) is experimental at /;
};

1;

$ perl -e 'use v5.10; given (12) { when (12) { print "Hello World\n" }}'
given is experimental at -e line 1.
when is experimental at -e line 1.
Hello World

$ export PERL5OPT=-MMonkey::SilenceSwitchWarning

$ perl -e 'use v5.10; given (12) { when (12) { print "Hello World\n" }}'
Hello World