SPUG: Introspective parameters... Can a parameter know it's argument's name from the caller's perspective?

Michael R. Wolf MichaelRWolf at att.net
Fri Jun 27 17:22:37 PDT 2008

A colleague just asked a question that's related to a question I've had for
years, so here goes my question.

Is there some way that a parameter can know the name of the argument from
the perspective of the caller?

I'd like to do something like this:

($first_name, $last_name, $favorite_language) = qw(Michael Wolf Perl);

foreach $variable first_name, $last_name, $favorite_language) {

And get output like this...

$first_name			(in namespace 'main::') has a value of
$last_name			(in namespace 'main::') has a value of
$favorite_language 	(in namespace 'main::') has a value of 'Perl'

I guess I'm looking for the ability to do introspection on elements of @_.
It might look something like this (in a pseudo-Perl syntax).

sub debug_blather {
    foreach my $i (0 .. $#_) { # Ewww, that's ugly!!!
        my $vn  = $_[$i].variable_name();
        my $ns  = $_[$i].namespace();
        my $val = $_[$i].value();
    my $fmt = '...';
    printf $fmt, $vn, $ns, $val;


Name and value are all I really care about, but other attributes might be
nice (namespace, reference count, etc.).

The big point is that I'd like to pass *one* thing, not two.  I can figure
out how to pass a variable (as a symbol) *and* its name (as a string), but
that's double (i.e. redundant (i.e. annoying and fragile)) work!  It's not a
DRY (Don't Repeat Yourself) way to work.

And I don't want to resort to hash builders that rely on symbolic variables
because I don't want to deal with strings when I'm really dealing with
identifiers.  Symbol table hashes scare me a bit because they break when my
code crashes.  They're hard to debug.  And I don't know how to do lexicals.
But mostly I want to avoid it because it feels like symbolic references are
a hack (even though I know I could parameterize that hack with __PACKAGE__
and a slew of strings).


P.S.  Is this something that's coming in Perl6?  If so, every day after
Perl6 will be Christmas!!!  :-)

Michael R. Wolf
    All mammals learn by playing!
        MichaelRWolf at att.net

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