(nearly) readonly globals

haoess has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I played a little bit with the vars listed in perlvar, and there are some inconsistent behaviours (using v5.10.0). Before filling a bug report, I would like to discuss these issues:

% perl -e '$$=1'
Modification of a read-only value attempted at -e line 1.

% perl -e 'local $$=1'

%
[download]

$$ is listed as read-only.

Same is for other special globals like $], $^{TAINT}, $^{UNICODE}, and $^V.

Is there a bug? Are the docs ambiguous?

-- Frank

Comment on (nearly) readonly globals Select or Download Code

Replies are listed 'Best First'.
Re: (nearly) readonly globals by BrowserUk (Patriarch) on Jan 19, 2009 at 20:18 UTC
Is there a bug? Are the docs ambiguous? No. And No. Using local creates a temporary instance of the named variable, and you can do what you like with it. That WAD (Working As Designed) Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^2: (nearly) readonly globals by haoess (Curate) on Jan 19, 2009 at 20:32 UTC
Using local creates a temporary instance of the named variable, and you can do what you like with it. But this does not apply to all special globals, i.e.: `% perl -e 'local $1 = 1' Modification of a read-only value attempted at -e line 1. % perl -e 'local $^S = 1' Modification of a read-only value attempted at -e line 1.` [download] -- Frank	[reply] [d/l]
Re^3: (nearly) readonly globals by Corion (Patriarch) on Jan 19, 2009 at 20:35 UTC
Yes - see local, resp. the documentation referenced by it, Private Variables via my() in perlsub.	[reply]
Re^4: (nearly) readonly globals by haoess (Curate) on Jan 26, 2009 at 18:49 UTC

Back to Seekers of Perl Wisdom