From mike808@mo.net

The relevant section of code from constant.pm v1.00 from perl 5.005_03​:

sub import {
  my $class = shift;
  my $name = shift or return; # Ignore 'use constant;'
  croak qq{Can't define "$name" as constant} .
  qq{ (name contains invalid characters or is empty)}
  unless $name =~ /^[^\W_0-9]\w*$/;

The RE used to validate names is broken for several perfectly
valid "constants", namely those that start with underbars.

  use constant qw( _MYCONSTANT => 4 ); # busted

I propose an improved RE as follows​:

  unless $name =~ /^(\w{2,}|[^\W_0-9AB])$/;

I added in preventing A and B being used as constants, as I don't like the
ability to say 'use constant qw( A => 4 );' since you're messing with the
globs associated with $A and $B used in the infamous 'sort' operator.
A slip of the $ will hose your sort. We're really trying to prevent
constants that conflict with the builtin global variables, right?
($_, $0, $1, $2, $3, $4, $5, $6, $7, $8, $9)
I'd just like to see $A and $B in that list, too.

The background on how I found this problem is that I use a derived
constant.pm that also exports the appropriate value as the appropriate
symbol, allowing faster access directly via the symbol for those who
want to.

i.e. 'use MyConstant TEN => 10;' also does an extra '$TEN = 10;'
step. It also creates the appropriate types when handed refs.
i.e. 'use MyConstant DIGITS => \[ 0 .. 9 ];' also does an extra
'@​DIGITS = (0..9);' so you don't have to access only via a function
interface.

But, that's *my* version of constant.pm, and I found it handy, and
not really anything to do with the CORE constant.pm. Just some background
on how I found the bug.

Michael
mike808@​mo.net

From [Unknown Contact. See original ticket]

On Sat, 6 Nov 1999, Michael King wrote​:

croak qq\{Can't define "$name" as constant\} \.
        qq\{ \(name contains invalid characters or is empty\)\}
    unless $name =~ /^\[^\\W\_0\-9\]\\w\*$/;

The RE used to validate names is broken for several perfectly
valid "constants", namely those that start with underbars.

Not broken; intentional. (Although I can't recall at the moment why in the
world I didn't simply use [A-Z] as that character class.... Maybe I was
thinking obfuscated thoughts. :-) As the docs say​:

  Constant names must begin with a letter.

Names beginning with an underbar are implicitly "reserved for future
expansion".

I propose an improved RE as follows​:

unless $name =~ /^(\w{2,}|[^\W_0-9AB])$/;

I added in preventing A and B being used as constants, as I don't like the
ability to say 'use constant qw( A => 4 );' since you're messing with the
globs associated with $A and $B used in the infamous 'sort' operator.

You seem to be confused; sort doesn't use $A and $B.

A slip of the $ will hose your sort. We're really trying to prevent
constants that conflict with the builtin global variables, right?

Nope. I merely wanted to reserve names starting with an underscore, so
that we'd have a class of such names to draw upon. Note that this
precludes a constant named __LINE__, for example. On the other hand, names
like BEGIN and ARGV are not precluded by this mechanism, but I still hope
no one will choose those as constant names....

Cheers!

--
Tom Phoenix Perl Training and Hacking Esperanto
Randal Schwartz Case​: http​://www.rahul.net/jeffrey/ovs/