in reply to Re^2: Possible useless use of map
in thread Possible useless use of map

perl590delta says map in void context is no longer expensive. map is now context aware, and will not construct a list if called in void context.

if there is no list, why is there list context?

Replies are listed 'Best First'.
Re^4: Possible useless use of map
by JavaFan (Canon) on Mar 18, 2010 at 15:04 UTC
    Just like about any other operator in Perl, map imposes a certain context on its operands, regardless of the context it itself is in. In: 
    map {$hash->{foo}} 1;

    [download]
    there are actually two lists, both containing a single element: the first list consists of $hash->{foo}, the second of 1.

    Think of it this way, if map would not provide list context to its inner block, the following wouldn't do what it does now: 

    %h = map {$_ => 1} qw[foo bar baz];

    [download]
[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom