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

How do we determine the type of a variable?
Isn't there any mechanism that can (politely) determine the type? (rather than using if defined() bla,bla,bla). Just wondering, though :)
  • Comment on What type are you? Mr Hash, Sir Array, or Miss Scalar?

Replies are listed 'Best First'.
Re: What type are you? Mr Hash, Sir Array, or Miss Scalar?
by hv (Prior) on May 12, 2004 at 14:27 UTC

    The Scalar::Util module has a function 'reftype':

    reftype EXPR

    If EXPR evaluates to a reference the type of the variable referenced is returned. Otherwise "undef" is returned.

    $type = reftype "string";           # undef
$type = reftype \$var;              # SCALAR
$type = reftype [];                 # ARRAY

$obj  = bless {}, "Foo";
$type = reftype $obj;               # HASH

    [download]

    Hugo

[reply]
[d/l]

      The builtin ref does this just fine for unblessed references. And unless you're going to be impolite and break encapsulation you may not want to go mucking about with other class' internals.

[reply]
[d/l]
      Ahhh, thanx, or else i will looked so DUMB :)
      Yes, i mean programatically, not me identifying variables (i know that, already).
      This is important when we using reference, since i need to know what the reference is pointing to...
[reply]

        have a look at   perldoc -f ref,   as Fletch already pointed out.

        Cheers, Sören

[reply]
      I've tried it out, but why is this doesn't work?
      I've used ref instead, but never on advanced level (on class etc.
[reply]
Re: What type are you? Mr Hash, Sir Array, or Miss Scalar?
by Limbic~Region (Chancellor) on May 12, 2004 at 14:28 UTC
    Doraemon,
    There is a way to tell a variable's type by using defined() bla,bla,bla? That is news to me.

    I am going to assume you mean some variable seen by your program that comes externally. If it was your own code you would only need to look at the sigil ( % => hash, $ => scalar, @ => array). If that is the case then you could probably get away with using ref (see perldoc -f ref). There are certainly limitations in ref, but I think it will fit your immediate needs.

    Cheers - L~R
[reply]
      defined() bla,bla,bla? yeah, right!
      Just a silly joke. Never seriously thought about that (harhar)
      But i've tried the ref, and it works just fine...problem solved
[reply]

        ref is correct, however you can do it yourself if you want to .. (don't know why you would) you can 

        my %test = ('test1'=>'value',
            'test2'=>'value');

my $hash_ref = \%test;

print "hash ref" if($hash_ref =~ m{HASH});

        [download]
        I used that once(before I knew about ref). I don't know if that's horribly bad practice or not, but it works. So basically you could go to the trouble (again I don't know why you would want to) of setting up your own ref via a case statement of regex's

        Grygonos
[reply]
[d/l]
Re: What type are you? Mr Hash, Sir Array, or Miss Scalar?
by haoess (Curate) on May 12, 2004 at 14:26 UTC

    I don't see any problem. A variable containing an array is named @array, a hash variable is named %hash, and a scalar variable is, you guess it, $scalar.

    You should tell us what you want to do more exactly.

    -- Frank

[reply]
      Say that, to someone who don't know what Perl is :)
      Just kidding. What i meant, 
      # type = what_type($ref);

      [download]
[reply]
[d/l]

Back to Seekers of Perl Wisdom