perlquestion
moritz
<p>At $dayjob I'm working on a project where the home-grown error reporting module occasionally warns <c>Use of "goto" to jump into a construct is deprecated</c>
<p>So now I'm trying to find out how exactly [doc://goto] LABEL works, in order to assess whether the whole error reporting module needs to be rewritten. And I found no documentation.
<p>The closest I found was [id://508852|"goto only searches the immediate call stack for labels"], but this alone doesn't explain how "jump into a construct" can happen at all -- if it only searched the caller's scope and the caller's caller's scope etc. for the label, it would never find label from inside a construct that's not in dyanmic call chain.
<p>Some curious experiments:
<code>
$ perl -wE 'if (0) { label: say 1 }; goto label'
Can't find label label at -e line 1.
$ perl -wE 'if (1) { label: say 1;}; goto label'
Use of "goto" to jump into a construct is deprecated at -e line 1.
1
Use of "goto" to jump into a construct is deprecated at -e line 1.
1
^C # aborted, because it loops
</code>
<p>So apparently, the construct containing the label has to have been executed once.
<p>This works:
<code>
#!/usr/bin/perl
use strict;
use warnings;
use 5.014;
sub f {
my $arg = shift;
if ($arg == 0) {
label:
say 'here';
}
elsif ($arg == 1) {
# don't execute a branch with 'label:'
}
else {
goto label
}
}
f($_) for 0..2;
__END__
here
here
</code>
<p>Whereas this one dies:
<code>
$ perl -wE 'sub g() { label: say "here" }; g; goto label'
here
Can't find label label at -e line 1.
</code>
<p>I have trouble finding a clear mental model that can help me to explain all of this behavior. Who can help?</p>
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