Re^3: How to differentiate hash reference and object reference?

My main problem with it is isn't so much the wording, but the fact that it doesn't even say which argument caused the problem.

Sure it does. the message says

Can't call method "isa" on unblessed reference at unblessedWantBetterError.t line 10.

Which tells us that on line 10 some $var is being used as an object in a method call and the content of $var is not actually an object. When we look at line 10 we see

die "not a foo" unless $obj->isa('foo'); #the error I want
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which tells us that the $var in question is called $obj.

Now presumably you are doing this because later on you have code that does something like

$obj->do_something($useful);
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But what do you gain? In this situation you would see the same error you are now just on the actual line where the actual code is being used, and not on some validation code.

So IMO you gain nothing but code complexity and you tie the hands of your codes consumers because they can't drop in a different object with a compatible interface. So IOW, you have made your code less usable and robust than more.

---
$world=~s/war/peace/g

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Re^4: How to differentiate hash reference and object reference? by xdg (Monsignor) on Aug 31, 2005 at 14:57 UTC
Not sure I agree if this is in the context of argument checking -- in which case it should be used with `croak` (from Carp) and not `die`. If the OP is writing a subroutine that takes an argument and then uses that argument to call a method defined for objects of type 'foo', then not checking the parameter means potentially dying with an error message pointing to the line in the OP's subroutine, not pointing to where the subroutine was called with an invalid argument: `sub wibble { my ($self, $obj) = @_; croak "Argument to wibble must be a 'foo' object" if ! ( blessed $obj and $obj->isa('foo') ); if ( $obj->wobble() eq 'spoon' ) { # handle spoon } }` [download] Or, as diotalevi said, use Params::Validate. -xdg Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.	[reply] [d/l] [select]

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Re^4: How to differentiate hash reference and object reference?
by xdg (Monsignor) on Aug 31, 2005 at 14:57 UTC

Not sure I agree if this is in the context of argument checking -- in which case it should be used with croak (from Carp) and not die.

If the OP is writing a subroutine that takes an argument and then uses that argument to call a method defined for objects of type 'foo', then not checking the parameter means potentially dying with an error message pointing to the line in the OP's subroutine, not pointing to where the subroutine was called with an invalid argument:

sub wibble {
    my ($self, $obj) = @_;
    croak "Argument to wibble must be a 'foo' object"
        if ! ( blessed $obj and $obj->isa('foo') );
    if ( $obj->wobble() eq 'spoon' ) {
      # handle spoon
    }
}
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Or, as diotalevi said, use Params::Validate.

-xdg

Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

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