in reply to how to call a sub via variable in library

$self->{&{\&{$testname}}}->($system); #system is hashref

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... 
Use of uninitialized value $self in concatenation (.) or string
Can't call method "_idown" on an undefined value
Can't call method "_idown" on an undefined value

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The errors suggest that at some point you are invoking one of your methods without argument, thus $self is never initialized. Carp can be very helpful here for recovering the call stack where the error is actually happening, in the calling routine. You could also manually construct a relevant error using caller: 
sub method {
    my $self = shift or die join(", ", caller()), "\n";
...
}

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If I've misdiagnosed the issue (which is plausible given how complex your invocation is), you probably want to learn How can I visualize my complex data structure?.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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Re^2: how to call a sub via variable in library
by Anonymous Monk on Nov 17, 2014 at 19:09 UTC
    $self is perhaps initialized, but 
    no strict 'refs';
$self->{ &{$testcase} }

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    (I mean, the original, obfuscated version) is probably undef... But I'm no going to read this code any futher, frankly.
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      That was my original thought, and then I saw Use of uninitialized value $self in concatenation (.) or string That's why I think my $self = shift or confess '$self undef'; is probably the best bet. I should point out that the $self that is uninitialized may not be the $self in the grotesque expression above.

      #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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