[Pdx-pm] Musings on operator overloading

[Jonathan Leto]

Howdy Folks,

[snip]
>  Note that even with mathematical abstractions, there are cases
>  where scope-bound overloading is a win over type-bound
>  overloading. Consider a hypothetical Math::Symbolic that lets you
>  do something like this:
>
>     my $x = Math::Symbolic->new();
>     print +( $x**2 + 4 * $x + 3 )->derivative( $x );
>
>  I hope it?s obvious how such a thing would me implemented. Now,
>  if you used type-bound overloading, then the following two
>  expressions cannot yield the same result:
>
>     ( 2 / 3 ) * $x
>     2 * $x / 3
>
>  But if overloading was scope-bound, they would!
[snip]

This piqued my interest, so I attempted to exhibit the problem with
Math::MatrixReal (which uses a fair bit of op overloading)  :

#!/usr/bin/perl -w
use strict;
use Math::MatrixReal;
# Example code to show type bound operator overloading
# that returns the same stuff

my $matrix = Math::MatrixReal->new_from_rows([[3,6,9]]);
my $a = (2/3) * $matrix;
my $b = 2 * $matrix / 3;
my $c = 2 * (+$matrix) / 3;
my $d = (2/3) * (+$matrix);

print "\$a is a " . (ref $a) . "\n";
print "\$b is a " . (ref $b) . "\n";
print "\$c is a " . (ref $c) . "\n";
print "\$d is a " . (ref $d) . "\n";
print "\$a=\n";
print $a;
print "\$b=\n";
print $b;
print "\$c=\n";
print $c;
print "\$d=\n";
print $d;

Which outputs:

$a is a Math::MatrixReal
$b is a Math::MatrixReal
$c is a Math::MatrixReal
$d is a Math::MatrixReal
$a=
[  2.000000000000E+00  4.000000000000E+00  6.000000000000E+00 ]
$b=
[  2.000000000000E+00  4.000000000000E+00  6.000000000000E+00 ]
$c=
[  2.000000000000E+00  4.000000000000E+00  6.000000000000E+00 ]
$d=
[  2.000000000000E+00  4.000000000000E+00  6.000000000000E+00 ]


Am I missing something?

 The current source for Math::MatrixReal is at
http://leto.net/svn/Math-MatrixReal/

and the source to that example can be found at
http://leto.net/svn/util/trunk/examples/ .

-- 

[---------------------]
   Jonathan Leto
jaleto at gmail.com
   503.928.0609