Question

It seems that one can't set a WebPreferences variable to zero ('0'). It always evaluates to the empty string "". There's a fix in the Answer section, below.

• TWiki version: 01 Sep 2001 release
• Web server: Apache 1.3.x
• Server OS: Linux 2.2.14
• Web browser: Opera, Netscape, Mozilla, Lynx (all Linux)
• Client OS: Linux 2.2.14

-- TrippLilley - 15 Nov 2001

Answer

TWiki::Prefs::getPrefsFromTopic uses this Perl idiom when it's evaluating preference variable values:

   $value = $2 || "";

The problem is that the assignment will fall through to the empty string ("") whenever $2 is false, which, by Perl's definition of "false", means whenever $2 is undefined, the empty string, or zero (0).

The fix is to check whether or not $2 is defined, since that's the only case for which we really want to force the empty string:

   $value = defined $2 ? $2 : "";

-- TrippLilley - 15 Nov 2001

Thanks for reporting. Copied it over to the Codev web as bug Codev.VariablesCantBeSetToZero

-- PeterThoeny - 16 Nov 2001