bv has asked for the wisdom of the Perl Monks concerning the following question:

So I found what I believe to be a bug in YAML::Any, specifically in the Dump function, but I suspect that the nearly identical code in DumpFile, Load, and LoadFile are also buggy. The intention of the code in question is to apply the settings of the $YAML::Option global options to the chosen implementation of YAML (in my case, YAML::XS). Here is the code, with my debug statements marked:

sub Dump {
    no strict 'refs';
    my $implementation = __PACKAGE__->implementation;
    my $debug; # My own debug variable
    for my $option (@dump_options) {
        my $var = "$implementation\::$option";
        $debug = $var if $var =~/UseCode/; #the option I wish to set
        my $value = $$var;
        local $$var; # <-- PROBLEM! Local to "for", not "sub"
        $$var = defined $value ? $value : ${"YAML::$option"};
        # Here I print out the option in each iteration of the loop
        print STDERR "$debug = $$debug\n";
    }
    # And the final value:
    print STDERR "FINAL: $debug = $$debug\n";
    return &{"$implementation\::Dump"}(@_);
}

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My test code:

#!/usr/bin/perl
use strict;
use warnings;
use YAML::Any;

local $YAML::UseCode=1;

my $input = sub {
    print "Enter a value: ";
    return chomp (my $ret = <>);
};

print Dump $input;

__END__
Name "YAML::UseCode" used only once: possible typo at test.pl line 7.
YAML::XS::UseCode = 1
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
YAML::XS::UseCode = 
FINAL: YAML::XS::UseCode = 
--- !!perl/code '{ "DUMMY" }'

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The "Name used only once" warning is not the issue, since I get the same warning when setting $YAML::XS::UseCode directly, and the output is what I would expect (The output of B::Deparse on the CODE reference);

What I believe is the issue is that each global option is localized within the for loop, and immediately returns to its previous value upon the next iteration. What I need is a solution to localize the value such that it stays set for the function call that is returned in the last line. So my questions are twofold:

  1. How do I set the value for $YAML::UseCode and have it apply to whatever implementation YAML::Any has chosen, AND
  2. How do I go about getting this (I think) bug fixed in YAML::Any?

Thanks much! My environment: YAML-0.70, YAML-LibYAML-0.32, "This is perl, v5.10.0 built for i486-linux-gnu-thread-multi"

UPDATE: My workaround is to use YAML::Any's implementation() method and cheat with strict refs:

#!/usr/bin/perl
use warnings;
use YAML::Any;

local ${YAML::Any->implementation()."::UseCode"}=1;
# can't use strict before this because of refs
use strict;

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@_=qw;
Just another Perl hacker,;
;$_=q=print
"@_"= and eval;

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Replies are listed 'Best First'.
Re: Bug in YAML::Any - What to do?
by ikegami (Patriarch) on Dec 15, 2009 at 00:01 UTC
    Icky hack (local ... for ...;): 
    sub Dump {
    my @opts;
    for my $option (@dump_options) {
        no strict 'refs';
        my $ref = \${$implementation.'::'.$option};
        push @opts, [ $ref =>
            defined($$ref) ? $$ref : ${"YAML::$option"},
        ];
    }
    local ${$_->[0]} = $_->[1] for @opts;
    return &{"$implementation\::Dump"};
}

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    Sticking to something that won't break: 

    {
    package YAML::OnScopeExit;
    sub DESTROY { ${ shift() }->() }
}

sub _on_scope_exit(&) {
    my ($sub) = @_;
    return bless(\$sub, 'YAML::OnScopeExit');
}

sub Dump {
    my @opts;
    for my $option (@dump_options) {
        no strict 'refs';
        my $ref = \${$implementation.'::'.$option};
        push @opts, [ $ref =>
            defined($$ref) ? $$ref : ${"YAML::$option"},
            $$ref,
        ];
    }

    my $sentinel = _on_scope_exit {
        ${$_->[0]} = $_->[2] for @opts;
    };

    ${$_->[0]} = $_->[1] for @opts;

    return &{"$implementation\::Dump"};
}

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    Both untested.

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Re: Bug in YAML::Any - What to do?
by zwon (Abbot) on Dec 14, 2009 at 23:30 UTC
    How do I go about getting this (I think) bug fixed in YAML::Any?

    Go to YAML::Any cpan page, follow "Report Bug" link and submit bug description. If you can fix the bug attach the patch. It is a good idea to check that this bag has not yet been reported by somebody else, there are a lot of bugs in the YAML::Any RT.

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Re: Bug in YAML::Any - What to do?
by Anonymous Monk on Dec 14, 2009 at 23:23 UTC
    yup, thats a bug, to fix you can put references into array, then local 
    sub Dump {
    my @vals ;
    my @opts ;
    for my $option (@dump_options) {
        no strict 'refs';
        my $var = \${"$implementation\::$option"};
        push @opts, $var;
        push @vals, defined $value ? $value : ${"YAML::$option"};
    }
    local (@opts) = @vals;
    return &{"$implementation\::Dump"}(@_);
}

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      That attempts to localise @opts, not the scalars referenced by the elements of @opts.

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