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Postings from July 2001
On Tue, Jul 24, 2001 at 09:32:54AM +0100, Nick Ing-Simmons wrote:
> my %hash = (a => 1, b => 2);
> my $ref = \$hash;
> readonly \%hash; # clamped
C<readonly %hash> should be achievable by simply using the \% prototype.
> $hash{'a'} = 10; # okay
So we can change the values...
> $hash{'c'} = 30; # dies "Attempt to add key to readonly hash"
> delete $hash{'b'}; # dies "Attempt to delete key from readonly hash"
...but not delete the key. That seems a little odd, since you're not
protecting much and it makes the normal delete/exists combination not
work. Pseudo-hashes had the same problem pre-5.6 and it was very
annoying.
Just want to reiterate the point that if we can change the value of a
key, we should be able to delete the key *and* reinstate it.
my %hash = (a => 1, b => 2);
readonly %hash;
$hash{a} = "foo";
delete $hash{a};
$hash{a} = "bar";
All good. Jeff came up with a workable internal solution by delete()
not actually deleting the key internally, but simply putting a magic
scalar flag on the value being deleted and having exists() look for
that on readonly hashes.
> readonly(\$_) foreach values %hash; # readonly - fix the values
> $hash{'a'} = 15; # dies "Attempt to modify readonly value"
Here, C<delete $hash{a}> would be an error.
--
Michael G. Schwern <schwern@pobox.com> http://www.pobox.com/~schwern/
Perl6 Quality Assurance <perl-qa@perl.org> Kwalitee Is Job One
grep { ref and ref !~ /^[A-Z]+$/ } kill 9, @ARGV;
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