use constant {
    OBJECT => 0,
    ARG0 => 1,
    ARG1 => 2,
};
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Then, your line is essentially like:

    my ($self, $body, $wheel_id) = @_[0, 1, 2];
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UPDATE: see POE::Session

The constants were confusing me. Thanks.

Neil Watson
watson-wilson.ca

Further to toolic's reply: the expression  @_[0, 1, 2] is an array slice (see Slices in perldata). Don't be thrown by the  _ (underscore): that's a perfectly valid (special) variable name.

When you encounter things like this in the future, the Debugger is very useful. In particular, look at the X vars... (or V Package::Name vars...) commands. Try, for example,

  DB<1> X OBJECT
$OBJECT = 123
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There's nothing special about constants. All that constant.pm does is create a method in the package that returns the value you gave, by cleverly using import through use. Here's the relevant parts from constant.pm in 5.12.3:

#=====================================================================
+==
# import() - import symbols into user's namespace
#
# What we actually do is define a function in the caller's namespace
# which returns the value. The function we create will normally
# be inlined as a constant, thereby avoiding further sub calling 
# overhead.
#=====================================================================
+==
sub import {
    #...

    #note: $full_name is set to "Package_I_Was_Called_From::ConstantNa
+me", for each constant you provide

    #if you have a scalar, it basically does
    *$full_name = sub () { $scalar };
    #and if you have an array:
    *$full_name = sub () { @list };

    #...
}
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Note: In the debugger output above, you may have noticed that it appeared as a regular variable. Indeed, in Perl 5.8 (as I understand it), constant.pm had some magic added to it so that scalars are simply added into the symbol table, appearing to be a package variable. Still, you can't really use them as variables, as you can observe here:

  DB<6> x &OBJECT
0  123

  DB<7> x $OBJECT
0  undef
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