This has bothered me far more than it should. I quite often end up writing test code that looks like this:
{
my @log = ();
no warnings 'redefine';
*Some::Package::some_func = sub { push @log, [@_] };
sub get_log {
my @old_log = @log;
@log = ();
return @old_log;
}
}
# Then some tests that call subroutines that end up calling some_func.
The idea is to monkeypatch (Perl word of the week) the module I'm testing so I can make sure it calls some_func with the right arguments. For example with TextMate::JumpTo I wanted to test that it was going to invoke /usr/bin/open with the correct args - without actually going through with it and opening something. I didn't want the tests to spew a bunch of random windows into the user's text editor.
None of that is what bothers me. What I find troubling is that get_log is five lines of code just to read and reset the contents of a list. That's really quite upsetting, right?
Today I decided I could endure it no longer (I may be being a little theatrical here) so I spent some time thinking about it. Ideally I'd like to do away with the temporary variable altogether but I can't see a way to do that. Instead I've settled for this:
sub get_log { ( my @got, @log ) = @log }
It's not especially pretty but it's better. That temporary still bugs me though...
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I think this will do it:
sub get_log { return splice @log }
Just make sure you use it in list context, though.
-- dagolden
Re:splice?
AndyArmstrong on 2008-01-19T23:05:16
Lovely!
You don't even need the return:
sub get_log { splice @log }That is a hack of great beauty. Thanks David
:) Re:splice?
dagolden on 2008-01-19T23:44:40
I only stuck the return in because I thought you were a Perl::Critic kinda guy.;-)
-- dagoldenRe:splice?
AndyArmstrong on 2008-01-20T00:26:21
I have mixed feelings about Perl::Critic. In any event, today I'm a do whatever feels good kinda guy:) Re:splice?
sigzero on 2008-01-21T15:08:50
Perl::Critic is a Perl "advisor" for me. I look at what it spits out and decide on my own if I want to "conform". I have PBP on my desk so I can read up on why it wants me to do it a certain way.
This isn’t better, but in the spirit of TMTOWTDI and of the select idiom from perldoc -q unbuffer…
sub get_log { @{ ( [@log], @log=() )[0] } }
Or to do away with the array-copy, assuming you have set up with “my $log = []” instead:
sub get_log { @{ ( \@$log, $log=[] )[0] } }
The \@$ construction is there to force Perl to make a new copy of the array reference in $log. That way the first list element is a copy of $log instead of an alias, and therefore unaffected by the overwriting of $log in the next expression.
But the splice solution is lightyears ahead.
You can also do this with delete instead of splice:
sub get_log { delete @log[0.. $#log] }
It's slightly slower than splice but you may consider it's closer to documenting your intent.
Re:delete Works Too
AndyArmstrong on 2008-01-20T11:32:36
We better not let any civilians see this thread otherwise Perl will get a bad name:)
