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Postings from October 2003
On Thu, Oct 09, 2003 at 12:29:30AM -0700, Stas Bekman <stas@stason.org> wrote:
> map { "$_" => 1 } (a..c);
>
> the first three lines are fine, the fourth produces an error:
>
> syntax error at /tmp/oops line 4, near "} ("
>
> what's wrong with $_ stringification as the key? and it only happens
> without () around the key/value pair.
>
> Originally I planned to do:
>
> ... = map { "key_$_" => 1 } (a..c);
>
> It seems to happen with all perls.
See perldoc -f map:
C<{> starts both hash references and blocks, so C<map { ...> could be either
the start of map BLOCK LIST or map EXPR, LIST. Because perl doesn't look
ahead for the closing C<}> it has to take a guess at which its dealing with
based what it finds just after the C<{>. Usually it gets it right, but if it
doesn't it won't realize something is wrong until it gets to the C<}> and
encounters the missing (or unexpected) comma. The syntax error will be
reported close to the C<}> but you'll need to change something near the C<{>
such as using a unary C<+> to give perl some help:
%hash = map { "\L$_", 1 } @array # perl guesses EXPR. wrong
%hash = map { +"\L$_", 1 } @array # perl guesses BLOCK. right
%hash = map { ("\L$_", 1) } @array # this also works
%hash = map { lc($_), 1 } @array # as does this.
%hash = map +( lc($_), 1 ), @array # this is EXPR and works!
%hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
or to force an anon hash constructor use C<+{>
@hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end
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