in reply to has it been blessed?

If you want to find out if an object is blessed and is a particular class, you would do something like this:

if ( UNIVERSAL::isa( $obj, 'Class::I::am::checking::for' )){
  $obj->invoke_method();
}

[download]

If you want to know if it is blessed into any old class at all, you could do something like this:

my $ref = ref($obj);
if ( $ref && ($ref !~ /^(SCALAR|HASH|ARRAY)$/) ) {
  $obj->invoke_method();
}

[download]

Replies are listed 'Best First'.
(tye)Re: has it been blessed?
by tye (Sage) on Mar 06, 2002 at 16:30 UTC

    For the first case, I'd add an additional check: 

        if(  ref($obj)  &&  UNIVERSAL::isa($obj,'Class')  ) {
        $obj->invoke_method();
    }

    [download]
    since UNIVERSAL::isa("main",'main') returns true even though "main" is not an object; UNIVERSAL::isa() works on class names as well.

    For your second test, I'd go a quite different route:     if(  ref($obj)  &&  UNIVERSAL::isa($obj,'UNIVERSAL')  ) { or, just to be shorter: 

        if(  ref($obj)  &&  UNIVERSAL::can($obj,'can')  ) {
# or
    if(  ref($obj)  &&  UNIVERSAL::can($obj,'isa')  ) {

    [download]
    You can also do:     use UNIVERSAL qw( isa can ); to make the above tests much shorter to write (allowing you to drop "UNIVERSAL::" in each).

    This all partially illustrates why it was a mistake for ref() to deal with both reference nature and blessedness nature. ref() should only return things like 'ARRAY' while a separate function, blessed() should tell you whether the item is a blessed reference or not (and probably return the package into which it was blessed, though using such information directly is usually a bad idea).

            - tye (but my friends call me "Tye")
[reply]
[d/l]
[select]
Re: Re: has it been blessed?
by rjray (Chaplain) on Mar 06, 2002 at 21:33 UTC

    The second test you pose is probably the more efficient, but you overlook a few candidates:

        my $ref;
    if ($ref = ref($obj) and $ref !~ /^(SCALAR|ARRAY|HASH|GLOB|Regexp)
+$/) {
        $obj->method();
    }

    [download]

    Technically, the Regexp references are objects, but they are part of the core, and wouldn't represent an application-defined class. Of course, you can drop that from the regex above, if you like.

    --rjray

[reply]
[d/l]
      Efficiency is nice, but there's something to be said for correctness as well. You've also forgotten REF, CODE, and LVALUE.

      Comparing the return value from ref to a list of known types is simply the wrong approach. Either you'll forget something, or a new type will be added in a future version and your code will break.

      Go with the UNIVERSAL::isa() approach. Really.

[reply]

        I agree, but to clarify, the best approach would seem to be:

            if (ref($obj) and UNIVERSAL::isa($obj, 'UNIVERSAL')) {
        ...
    }

        [download]

        Well, "best" in absence of the blessed primitive, of course...

        --rjray

[reply]
[d/l]

In Section Seekers of Perl Wisdom