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Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:
Hi,
here's an XS question this time regarding read-only variables...
In one of my "classes" my blessed thingy happens to be an HV which hold
information about a distinguished name (canonical format, abbreviated,
surname, given, common name, etc...).
i.e: print $name->{Common};
I'd like to be able to make that hash read-only and tried it (using SvREADONLY_on(HV)) but you can still
do this:
$name->{valueNotInHashInitially} = "Some Value";
You can do that even though Devel::Peek show the hash as having the READONLY
flag. I did set all the entries (SVs) in the hash to READONLY and that
worked.
ie: $name->{Common} = "New Value"; raises an error and dies.
Is there anything I can do so Perl also raise the same error when a user tries
to create new entries in my ReadOnly hash?
Thanks,
Christian Cloutier |
Re: XS ReadOnly HVs
by PodMaster (Abbot) on Apr 02, 2003 at 07:06 UTC
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I don't think you can do it in XS, at least not with normal hashes .... anyway, see Readonly and ex::constant::vars cause they do that.
update: Yup, magic is needed (man that sounds funny).
MJD says you
can't just make shit up and expect the computer to know what you mean, retardo!
I run a Win32 PPM
repository for perl 5.6x+5.8x. I take requests.
** The Third rule of perl club is a statement of fact: pod is sexy.
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Re: XS ReadOnly HVs
by robin (Chaplain) on Apr 03, 2003 at 10:37 UTC
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This is a very good question, and has been raised on p5p
in the past. As far as I know (which might not be far
enough - I'm doing more category theory than programming
these days) there is still no simple way to do what you
want.
The most concerted attempt to change this was made by
Jeff Friedl in 2001. Take a look at the threads starting
here,
here
and here. As you can see, the necessary code has all been written,
but doesn't seem to have been incorporated into perl.
You could try asking p5p about the status of this.
Update: On closer inspection, it seems that this
has been incorporated into Perl 5.8. Look at the
module Hash::Util. It seems that, in Perl 5.8,
the SvREADONLY flag does prevent new keys from
being added to a hash. What version of Perl are you using?
.robin. | [reply] |
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Robin,
Thanks a lot for pointing me in the right direction...
I am currently using 5.6.1 but will most certainly upgrade to 5.8.x.
So the only way of enforcing that behavior for hashes will be to require 5.8.0; in my modules?
That will prevent users with older perl from using it...
Any thoughts?
Chris.
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[d/l] |
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