Update: As Not_a_Number points out below, the behavior described in this post applies not only to 1 (as I originally stated), but to 0 as well. And, after reading merlyn's post, well, it looks like there's a huge number of constants—all those strings beginning with "di", "ds", or "ig"—that perl won't warn about when they are evaluated in a void context. See the code responsible for this behavior, kindly posted by AM.

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OK, here's another idle Perl arcana question. A scalar constant in a void context will result in a warning, unless this constant evaluates to a numeric value of 1; e.g.:

% perl -wce 5
Useless use of a constant in void context at -e line 1.
-e syntax OK
% perl -wce 1
-e syntax OK
% perl -wce '5**0'
-e syntax OK
% perl -wce 1.00
-e syntax OK
% perl -wce 'q(1)'
Useless use of a constant in void context at -e line 1.
-e syntax OK
[download]

Does anyone know the rationale for this special dispensation for (numeric) 1? The only one I can think of (and it's a pretty tortured one) is that it silences the warning that would have otherwise been triggered by the usual require-appeasing "1;" when one checks a module's syntax using perl -wc.

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