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Re: Conditional inheritance strategy

by JavaFan (Canon)
on Oct 27, 2010 at 13:02 UTC ( #867708=note: print w/replies, xml ) Need Help??


in reply to Conditional inheritance strategy

Is this a correct design to face this?
Not in general. @ISA is a package variable, it isn't bound to a specific instance. So, if you do:
my $x = My->new(source=>"xml"); my $y = My->new(source=>"json");
then now both $x and $y are instances of a class that inherits from My::JSON. If My::XML and My::JSON only contain _init, and this is only called from new, you're getting away with it, but if they also contain methods that will be called elsewhere from the program, behaviour may be unexpected.

Perhaps you can reverse the inheritance order:

package My::XML; use My; our @ISA = qw[My]; sub init {...} 1; package My::JSON; use My; our @ISA = qw[My]; sub init {...} 1; package My; sub new { my $class = shift; my $self = bless {}, $class; $self->init; $self; } 1; package main; use My::XML; use My::JSON; my $x = My::XML->new; my $y = My::JSON->new;

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Re^2: Conditional inheritance strategy
by citromatik (Curate) on Oct 27, 2010 at 13:32 UTC
    Not in general. @ISA is a package variable, it isn't bound to a specific instance. So, if you do:
    my $x = My->new(source=>"xml"); my $y = My->new(source=>"json");
    then now both $x and $y are instances of a class that inherits from My::JSON.

    Good point

    If My::XML and My::JSON only contain _init, and this is only called from new, you're getting away with it, but if they also contain methods that will be called elsewhere from the program, behaviour may be unexpected.

    Yes, My::XML and My::JSON only contain _init and this is only called from new, so this is not a problem, but I think that I will reverse the inheritance as suggested several times in this thread

    Thanks

    citromatik

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