That the point of map. It takes a list of inputs, and produces a different list from those inputs. It does so by applying the transformation function (the block or expression) to each input, and collecting the outputs of that function.

Examples:

my @uc = ( uc("abc"), uc("def") );

     |
     v

my @uc = map { uc($_) } "abc", "def";
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my %h = ( "abc" => 1, "def" => 1 );

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     v

my %h = map { $_ => 1 } "abc", "def";
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I didn't know that map could be used such a way (i.e. having an output instead of altering every item in a list)

Erm, that is what map is for! :) Perl::Critic even provides a ProhibitVoidMap policy to warn you of code that uses map in void context.

I suggest you follow the simple stylistic advice given in Effective Perl Programming in the item "Use foreach, map and grep as appropriate" namely:

• Use foreach to iterate read-only over each element of a list
• Use map to create a list based on the contents of another list
• Use foreach to modify elements of a list
• Use grep to select elements in a list