0: =pod
1: 
2: is_constant($sub_name) - returns true if subroutine is a 
3: constant, false if not.  $sub_name must be the fully 
4: qualified name (Package::name) of a subroutine.
5: 
6: =cut
7: 
8: sub is_constant {
9:     no strict 'refs';
10:     my $name = shift;
11:     my $code = *{$name}{CODE};
12: 
13:     # must have any empty prototype to be a constant
14:     my $proto = prototype($code);
15:     return 0 if defined $proto and length $proto;
16: 
17:     # attempt to redefine to itself - this will cause a 
18:     # warning for a real constant that starts with "Constant"
19:     my $is_const;
20:     {
21:         local $SIG{__WARN__} = sub { $is_const = 1 if $_[0] =~ /^Constant/ };
22:         eval { *{$name} = sub () { "TEST" } };
23:     }
24:         
25:     # set it back
26:     {
27:         no warnings;
28:         eval { *{$name} = $code; };
29:     }
30: 
31:     # all done
32:     return $is_const;
33: }