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Re: Concerning hash operations (appending, concatenating)

by japhy (Canon)
on Mar 24, 2005 at 16:53 UTC ( #442115=note: print w/ replies, xml ) Need Help??


in reply to Concerning hash operations (appending, concatenating)

The problem is that Perl doesn't abstract the concept of appending for its various containers (scalars, arrays, and hashes), because Perl isn't inherently OO. I don't know if Perl 6 is going this route, where you could say:

$foo.append($bar); @foo.append(@bar); %foo.append(%bar);
And in the same vein, perhaps:
$foo.prepend($bar); @foo.prepend(@bar); %foo.prepend(%bar);
In recent Perls, we can write this as:
# append($x, $y) appends $y to $x # etc. # prepend() left as a simple exercise to the reader sub append (\[$@%]\[$@%]) { use Scalar::Util 'reftype'; use Carp qw( croak ); my ($l, $lt, $r, $rt) = map { $_, reftype($_) } @_; if ($lt eq $rt) { if ($lt eq 'SCALAR') { $$l .= $$r; } elsif ($lt eq 'ARRAY') { push @$l, @$r; } elsif ($lt eq 'HASH') { @$l{keys %$r} = values %$r; } else { croak "append($lt,$rt) not implemented"; } } else { croak "append($lt,$rt) not implemented"; } }
I'd expect friction coming from the "what does append/prepend mean for hashes?" faction, but I'd say it's a matter of precedence. Appending to a hash, when there are duplicate keys, uses the new values, and prepending would use the old values.
_____________________________________________________
Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart


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