Your question is a little confusing (at least to me). 
my $obj = Some::Class->new();

[download]
returns a blessed reference so ref ($obj) returns the name
of the class into which the ref was blessed.

UPDATE: please ignore was having an acid flashback!

Your second examples are incorrect isa() does not
answer the question is this object this data type.
IT answers the question is the object an instance of class foo
either directly or by way of inheritance.
Assumes the isa() you refer to is UNIVERSAL->isa().
HASH, ARRAY and SCALAR are NOT Classes they
are data types.

That being said, is want you really want to determine the 'underlying' data type of the blessed reference ??

If so why not just create a 'type' method in the class.

mitd-Made in the Dark
I've always been astonished by the absurd turns
rivers have to make to flow under every bridge.

In reply to Re: How do I determine the underlying type of an Object? by mitd
in thread How do I determine the underlying type of an Object? by jaa

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