How do I test if a 'thing' is a hash (or array or scalar)?

[Anonymous Monk]

How do I test if a 'thing' is a hash (or array or scalar)?

Originally posted as a Categorized Question.

[merlyn]

If you have it in $foo, it's a scalar. It can't be an array or a hash, because Perl is strongly typed.

If you meant "how do I test whether a reference to {something} is a reference to a scalar/array/hash?", then look at the ref function.

[tye]

But ref() won't tell you whether a blessed reference is a reference to a scalar, array, hash, or other. A better approach is:

UNIVERSAL::isa( $ref, "HASH" )

        - tye (but my friends call me "Tye")

Q&A Editor comment: See Library entry: perlman:lib:UNIVERSAL

[chromatic]

When I find myself in this situation, I usually just do a regex for HASH or CODE or whatever. Seems to be more efficient than making UNIVERSAL check the (potentially tall) inheritance tree.

References to my objects tend to be of the form  One=SCALAR(0x80f11bc) or Two=CODE(0x80f7d30).

[tye]

To be clear, you are suggesting something like:

$ref =~ /HASH/

or

$ref =~ /(^|=)HASH\b/

which checks the "stringification" of the reference. But this fails for objects that have stringification overloaded. It is better than ref(), but I still don't want to make code that breaks for such cases. I have seen cases of this, but unfortunately I don't remember where. :(

If UNIVERSAL::isa() is a pig, then an efficient replacement needs to be provided (Hmmm... that would be an easy XS to write...).

I didn't think that UNIVERSAL::isa() would search the inheritance tree since whether a blessed reference is a hash or not has nothing to do with inheritance. I hadn't looked into how isa() is implemented. You'll have to read universal.c if you are that interested. I started to and realized I don't have that much time right now.

        - tye (but my friends call me "Tye")