in reply to Re: OO - problem with inheritance
in thread OO - problem with inheritance

> It sounds like you're wrestling with the question of how to create class data so that the accessors are inherited but not the data itself.
I would like the accessors _and_ data inherit.

In base_class is the big $parameter_config hashref. And there is a constructor new() which execlusively deals with this hashref. He gets his values by $parameter_config->{..}{..} and so on. But the other modules, which inherit from base_class only submit their changes to that huge config-hashref. Because this can't be done directly, I wrote two subroutines in base_class: valid_parameter and config_parameter. I want them to store the additional information in this hashref. But - and here is my problem - this hashref should be unique for each datatype/class. So I would like to access the hashref in base_class but the contents should be specific to the calling class.

I agree, that this is very naive. Now I'm searching for an other approach. Have you written my reply to Ilya's answer? I would like to use the last method: copy the hash and change it a little bit. But because it's an hashref, I think this won't work...

To your suggestion:
I need the %parameter_config hash before new() is called, because new() needs this information to figure out, if the parameters given to new() are correct. So I need code I can run when the class is loaded.

Thank you, good bye, Uwe

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Re: Re: Re: OO - problem with inheritance
by frag (Hermit) on Jan 14, 2002 at 21:43 UTC
    So I would like to access the hashref in base_class but the contents should be specific to the calling class.

    I'm a little confused about what you're doing. You want each change submitted to the base_class's %parameter_config for confirmation; after that, the actual values get stored in each subclass's own %parameter_config, right? If so, just change your accessors so that before fiddling with %sub_class::parameter_config it first messes with %base_class::parameter_config, to do whatever checking/storing you want done there, and then store the data in each individual subclass's hash. (Or, if you follow your new approach, replace "fiddling with %base_class::parameter_config" with "call validation methods from ValidateNewParameter". Same principle.)

    I need the %parameter_config hash before new() is called, because new() needs this information to figure out, if the parameters given to new() are correct. So I need code I can run when the class is loaded.

    OK, so put something like this at the start of each subclass: 

    use vars qw(%parameter_config); # or 'our' but NOT 'my', not if you
                                # use the approach I gave before
%parameter_config = &base_class::parameter_config;

    [download]
    And now each subclass has its own copy of %parameter_config. Just make sure that &base_class::parameter_config returns a copy of the hash.

    -- Frag.
    --
    "It's beat time, it's hop time, it's monk time!"

[reply]
[d/l]
      Hello Frag,
      thank you for your answer. I agree with you that I could solve my problem by copying the hash in ¶meter_config. But instead I go for ValidateNewParameter.
[reply]
        by copying the hash

        Note that just copying the hash doesn't work for data structure you have used. Values of hash are hashrefs themselves so new copy will reuse parts of copied data structure. Thus changes in copy of data structure affect original data structure.

        --
        Ilya Martynov (http://martynov.org/)

[reply]

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