Re^2: Unhappy returns

[Perl Mouse]

It's a tradeoff, and I'm glad Larry made the decision map can return lists of arbitrary length. My prime use of this feature is to create hashes:

    my %hash = map {($_, 1)} qw /foo bar baz/;

[Aristotle]

Yes – though that still only returns a fixed number of elements per evaluation. What about flattening data structures?

my @list = map @$_, @$lol;

I think that feature of map is one of the most useful things to have around for those occasions it’s called for.

[Keystroke]

Using map is a lot of overhead for just assigning to a hash.

use Benchmark;
timethese(1000, {
    'map1' => sub {
        my %str = map {($_,1)} (0..1024);
    },
    'arry' => sub {
        my %str = ();
        @str{0..1024} = (1)x1025;
    }
});

Benchmark: timing 1000 iterations of arry, map1...
      arry:  1 wallclock secs ( 1.36 usr +  0.00 sys =  1.36 CPU) @ 73
+5.29/s (n=1000)
      map1:  3 wallclock secs ( 3.11 usr +  0.00 sys =  3.11 CPU) @ 32
+1.54/s (n=1000)

[Perl Mouse]

That of course depends entirely on what you do with in the map. I used constant values of 1 just to illustrate my point, and to keep the example as simple as possible.

[dragonchild]

Overhead how? Depending on what I'm doing, hash-slicing might be harder to maintain than map.

my %is_month_abbrev = map { $_ => undef } qw( 
    jan feb mar apr may jun jul aug sep oct nov dec
);

# versus ...

my %is_month_abbrev;
@is_month_abbrev{ qw( jan feb mar apr may jun jul aug sep oct nov dec 
+) } = (undef) x 12;

# or, with an intermediate array ...

my @months = qw( jan feb mar apr may jun jul aug sep oct nov dec );
my %is_month_abbrev;
@is_month_abbrev{@months} = (undef) x @months;

Often, losing a few micro-seconds is worth readability and maintainability. In both the slicing solutions, I either needed a separate array or hard-coding a magic number. (The number of months in a year isn't always a given. Some calendars have as few as 10, others have up to 14, and still others vary from year to year.)