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wantarray() description in perlfunc as of v5.8.7

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From:
Flavio Poletti
Date:
July 26, 2005 09:19
Subject:
wantarray() description in perlfunc as of v5.8.7
Message ID:
28274.194.237.142.13.1122395397.squirrel@mail.polettix.it
Hi,

   I find the documentation for wantarray in perlfunc.pod a little obscure
in its current form (i.e. version 5.8.7).

The obscure passage is the following:

 wantarray()'s result is unspecified in the top level of a file,
 in a BEGIN , CHECK , INIT  or END  block, or in a DESTROY method.

All make sense to me except "top level of a file", which is obscure IMHO.
Could it be explained more in depth? My very issue regards the use of "do"
on a file: it currently seems to support wantarray correctly even "in the
top level of a file" (example at
http://www.perlmonks.org/?node_id=477801), but I'd like to know if this
still falls in the "unspecified behaviour" warning and, if yes, why.

To give you some background perspective, I saw some emails here in p5p
about the issues regarding END, INIT, etc. (for example at
http://www.mail-archive.com/perl5-porters@perl.org/msg83191.html); I tried
to ask at Perl Monks first (see http://www.perlmonks.org/?node_id=477759)
for explainations and suggestions for a modification proposal, but with no
luck.


#### Proposals #########

Unfortunately, my Perl Powers are too weak for me to propose something
100% correct and clear. But I want to be proactive and try to propose to
change "file" into "program":

 wantarray()'s result is unspecified in the top level of a program,
 in a BEGIN , CHECK , INIT  or END  block, or in a DESTROY method.


I think that it would be good to have some self-contained definition of
what the "context" is exactly - this is something really beyond my
strenghts (but see below for some effort :). Given such an explaination,
the docs could change as follows (note that I added the results of some
tests of mine):

 wantarray()'s result is unspecified wherever there is not
 a user reachable context, which happens in the top level
 of a program, in a BEGIN, CHECK, INIT or END block, or
 in a DESTROY method. See blah-blah-blah for the exact definition
 of context.


As I said, giving clear and exact explainations is far beyond my
possibilities. But I can write down something that, if true, could be used
to provide examples for this C<do> issues regarding the context.

 Note that you can still get a context in the top level of a file
 when you use C<do 'file.pl';>. In this case, in fact, the code inside
 I<file.pl> is provided a context according to the call to C<do>:

    my @a = do 'file.pl';  # array context provided
    my $s = do 'file.pl';  # scalar context provided
    do 'file.pl';          # void or "external" context provided

 Dealing with context, these calls to C<do 'file.pl'> are equivalent
 to sub calls; the last line, for example, could "inherit" the context
 when called as the final statement of a sub or of a file.


Excuse my verbosity, but I'm not anglophone - thus I'm not so good in
getting understood with fewer words :)

Best regards,

    Flavio.

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