Better way to test Object Inheritance?

throop has asked for the wisdom of the Perl Monks concerning the following question:

Is there a straightforward way to check if an instance inherits from a particular class?

I've put together something that works, but it uses eval to climb back through packages' @ISA variables. Can I get more elegant?

Here's the need. I'm modeling sentence structure. I have a base class, ucf::Constit::ScopeConstit; with other classes inheriting as below:

    ucf::Constit::ScopeConstit;
      ucf::Constit::NounCn;
        ucf::Constit::PrepCn;
          several other kinds of Prep
      ucf::Constit::VerbCn;
      ucf::Constit::ModifierCn;
[download]

I have $sentence, which an array of constit-instances, all drawn from these classes. I want derive a shorter array, $NPs, consisting of only those constits which inherit from ucf::Constit::NounCn. So, I need a function InheritsFrom($ObjRef, $className) which returns TRUE iff $ObjRef inherits from $className. I coded up this, which works:

package base::ObjInheritance;
use strict;
use Carp;
use Exporter;
our @ISA = qw(Exporter);
our @EXPORT = qw(InheritsFrom);
use List::Util qw(first);

sub InheritsFrom{
    my($ObjRef, $className) = @_;   # I"ve scrubbed the error checking
+ code for clarity
    my $oref = ref $ObjRef;   
    &IF1($oref, $className)}

sub IF1{
                                         # $ref and $className will bo
+th be strings, which name classes.
    my($ref, $className) = @_;
    return 1 if $ref eq $className;      # We've found an inheritance!
    my $isa = '@' . $ref . '::ISA';      # Rely on the ref being the p
+ackage
    my @parents = eval $isa;             # Find the @ISA for the packa
+ge and eval it
    foreach my $heather (@parents){      # Recurse on the parents
    next if $heather eq 'Exporter';
    if(&IF1($heather, $className)){
        return 1}};
    0}                  # Found no inheritance in this branch.
[download]

So now, I can find my $NPs

  my $NPs = [grep &InheritsFrom($_, 'ucf::Constit::NounCn'), @$sentenc
+e]
[download]

Was there a cleaner way to have done this, without using eval?

Thanks
throop

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Re: Better way to test Object Inheritance? by kcott (Archbishop) on Sep 10, 2013 at 20:03 UTC
G'day throop, "Is there a straightforward way to check if an instance inherits from a particular class?" Take a look at UNIVERSAL. In particular, the `isa` method: "When used as an instance or class method (`$obj->isa( TYPE )`), `isa` returns true if `$obj` is blessed into package `TYPE` or inherits from package `TYPE`." -- Ken	[reply] [d/l] [select]


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