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Re: [perl #114024] perl mistakenly warns when $] indexes a slice

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From:
Elizabeth Mattijsen
Date:
August 1, 2012 00:31
Subject:
Re: [perl #114024] perl mistakenly warns when $] indexes a slice
Message ID:
1D03BC96-93EF-4053-8B9E-CF9EF3EE1A81@dijkmat.nl
On Aug 1, 2012, at 8:05 AM, Father Chrysostomos via RT wrote:
> On Tue Jul 31 08:55:25 2012, sprout wrote:
>> $ ./perl -Ilib -Mwarnings=syntax -e '@a[]'
>> Scalar value @a[] better written as $a[] at -e line 1.
>> syntax error at -e line 1, near "[]"
>> Execution of -e aborted due to compilation errors.
>> 
>> We could change it to skip the warning for the empty string or an
>> initial alphanumeric character.  Instead of warning immediately, the
>> lexer could flag the op, and the compiler could then look to see whether
>> there is indeed just one kidop and warn.
>> 
>> I think that would work, without making the lexer’s heuristics overly
>> complex.
>> 
>> Is there anything obviously wrong with that?
> Yes: the source code cannot easily be accessed once one has an op.
> 
> Would it be acceptable to change the warning to use an ellipsis? 
> (Scalar value @a[...] better written as $a[...].)
> 
> Would it be acceptable to remove this warning altogether?  The only case
> that could cause a problem is @a[+foo], because foo could be called
> unexpectedly in list context.  But that is precisely the case in which
> perl cannot know that foo won’t return a list on purpose.  @a[0] is
> generally harmless.  Is this supposed to be newbie patrol (to stop them
> from using @a[0] all over the place)?

I wonder whether this warning shouldn't be removed on the grounds that:

1. it is valid Perl 6 syntax, so what are we teaching newbies anyway?
2. there is only a performance difference between $a[0] and @a[0], or am I missing something there?



Liz
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