2009/11/11 Uri Guttman <u...@stemsystems.com>:
>>>>>> "PP" == Philip Potter <philip.g.pot...@gmail.com> writes:
>
> PP> my %readfsgs_flags;
> PP> my @flags_to_copy = qw(limit); # can scale up by adding more hash
> keys here
> PP> @readfsgs_fla...@flags_to_copy} = @{$flag...@flags_to_copy};
> PP> my @results = readfsgs($testfilename, \%readfsgs_flags);
> PP> }
>
> PP> but this has a bug: if $flags doesn't contain limit, %readfsgs_flags
> PP> will contain (limit => undef); ie $readfsgs_flags will exist but be
> PP> undefined. It shouldn't exist.
>
> easy fix. just grep through all the keys you want and test for exists.
>
>
> my @flags_to_copy = grep { exists( $flags->{$_} } qw(limit);
>
> then the slice works as you have it and you only get flags you are
> interested in and also that exists coming in.
That fixes the major problem, thanks!
> you can also simplify the copy a little with a hash ref:
>
> my $readfsgs_flags = { map { $_ => $flags->{$_} } @flags_to_copy } ;
Is this really simpler than my version?
> PP> @readfsgs_fla...@flags_to_copy} = @{$flag...@flags_to_copy};
It took me a while to parse the map call, and the extra curlies from
the anonymous hash get confused with the code block curlies. Is this
map call a common technique for constructing subhashes (analogous to
subsets)?
Also, is the hash ref necessary? Would this also work?
my %readfsgs_flags = map { $_ => $flags->{$_} } @flags_to_copy;
> and if you feel like really combining lines (not so great in this case):
>
> my $readfsgs_flags = { map { $_ => $flags->{$_} }
> grep { exists( $flags->{$_} } qw(limit) ;
>
>
> or another cleaner way would be to put the exists inside the map:
>
> my $readfsgs_flags = {
> map { ( exists( $flags->{$_} ) ? $_ => $flags->{$_} : () } qw(limit) ;
I see what you've done there. I think you're right that it's probably
best in two statements -- after all, it's going to be two lines
whether it's two statements or one.
Phil
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