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Postings from February 2012
On Sun, Jun 12, 2011 at 04:12:31PM -0700, Father Chrysostomos wrote:
> $ perl5.14.0 -e 'continue;'
> syntax error at -e line 1, near "continue"
> Execution of -e aborted due to compilation errors.
>
> I thought the whole purpose of feature.pm was to avoid conflicts with
> user-defined subroutines. Since 'continue' is a syntax error anyway
> without feature.pm, should it be necessary to load feature.pm to get a
> bare 'continue' as a keyword (with its when-exiting meaning)?
>
> Making it the same as any other keyword, and not dependent upon
> feature.pm, actually simplifies the code in toke.c
I'm not convinced that this is a good thing. It turns a compile time
syntax error:
$ perl5.8.9 -cle 'use strict; continue;'
syntax error at -e line 1, near "; continue"-e had compilation errors.
into a run time error:
$ ./perl -Ilib -cle 'use strict; continue;'-e syntax OK
$ ./perl -Ilib -le 'use strict; continue;'
Can't "continue" outside a when block at -e line 1.
And it's not really helping anyone use a subroutine named continue, as it
turns out one *has* to use & syntax to call it:
$ perl5.8.9 -cle 'use strict; sub continue {print "Hi"}; continue;'
syntax error at -e line 1, near "; continue"
-e had compilation errors.
$ perl5.8.9 -cle 'use strict; sub continue {print "Hi"}; continue();'
syntax error at -e line 1, near "; continue"
-e had compilation errors.
$ perl5.8.9 -cle 'use strict; sub continue {print "Hi"}; &continue();'
-e syntax OK
again, all the compile time errors become run time errors:
$ ./perl -Ilib -cle 'use strict; sub continue {print "Hi"}; continue;'
-e syntax OK
$ ./perl -Ilib -cle 'use strict; sub continue {print "Hi"}; continue();'
-e syntax OK
$ ./perl -Ilib -cle 'use strict; sub continue {print "Hi"}; &continue();'
-e syntax OK
$ ./perl -Ilib -le 'use strict; sub continue {print "Hi"}; continue;'
Can't "continue" outside a when block at -e line 1.
$ ./perl -Ilib -le 'use strict; sub continue {print "Hi"}; continue();'
Can't "continue" outside a when block at -e line 1.
$ ./perl -Ilib -le 'use strict; sub continue {print "Hi"}; &continue();'
Hi
I can't actually work out what it now enables, that previously wasn't
possible, or wasn't easy.
I agree that simplifying toke.c (by 12 lines) is a win. But I don't think
it's enough of a win, given that it shunts error detection to runtime, and
means that the documentation has got just a bit more complex:
Except for C<continue>, these are available only if you enable the
C<"switch"> feature or use the C<CORE::> prefix.
See L<feature> and L<perlsyn/"Switch Statements">.
Alternately, include a C<use v5.10> or later to the current scope. In Perl
5.14 and earlier, C<continue> required the C<"switch"> feature, like the
other keywords.
A lot of people are each paying a tiny price for a small benefit to a small
number of core developers.
Nicholas Clark
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