map +

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

Hi all

I recently came across something like map + . I learnt the difference between map and map + is like, map returns a hash while map + return array of anonymous hash.

Can anyone of you can tell me in which context map and map + is used with examples ie; why we require a hash in one place and why an array of anonymous hash in another.

Thankyou

Comment on map +

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Re: map + by gellyfish (Monsignor) on Jun 21, 2005 at 09:23 UTC
Er `map +` is not a separate thing to `map` it is simply that on occasion the plus sign (the otherwise no-op unary addition ) might be necessary to disambiguate the bare block and prevent it from being parsed as an anonymous hash. /J\	[reply] [d/l] [select]
Re: map + by tlm (Prior) on Jun 21, 2005 at 11:07 UTC
The unary operator `+` is often used to disambiguate syntax that would otherwise confuse perl. In the case of `map` this can happen in two different situations. One is when the first non-whitespace character after the `map` keyword is a `(`. The other one is when this character is a `{` ... Read more... (4 kB) the lowliest monk	[reply] [d/l] [select]
Re: map + by borisz (Canon) on Jun 21, 2005 at 10:09 UTC
The + is just to point the perl parser into the right direction see map. `%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 "+{" @hashes = map +{ lc($_), 1 }, @array # EXPR, so needs , at end` [download] Boris	[reply] [d/l]