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I'm working through Hall and Schwartz's Effective Perl Programming: Writing Better Programs with Perl and had a small question about the passage below:
To a certain extent, idiom and style overlap. Some idioms, like print sort <>, are inarguable, but there are certainly gray areas:
foreach $key (sort keys %h) { print "$key: $h{$key}\n"; }
Print key-value pairs from %h one per line.
print map "$_: $h{$_}\n", sort keys %h;
Another way to print key-value pairs. The first example above is very plain Perl. It is efficient and readable and uses only basic features of the language. The second example is shorter and, some might argue, has a higher "cool factor" because it uses the nifty map operator and a list context in place of the mundane foreach loop in the first. However, you should consider yourself and your potential audience before leaving code like the second example for posterity, because it is definitely more obscure (but not that obscure) and might even be less efficient.
In my reading on perlmonks I've definitely noticed a bias towards the use of map and grep functions, and so I've been taking strides towards becoming more comfortable implementing them in my code (basic as it may be). Even so, I would like to understand in what ways the map version of the code above would be less efficient than the more verbose foreach loop? Is efficiency being sacrificed for the versatility/style of map? Is there a difference in efficiency at all? I assumed the two methods above to be interchangeable, but should I be being more selective of the situations where I use map?
The above segment is taken from Effective Perl Programming: Writing Better Programs with Perl By Joseph N. Hall, Randal L. Schwartz Publisher : Addison Wesley Pub Date : December 30, 1997 ISBN : 0-201-41975-0 and in no way my own.

In reply to Efficiency of map vs. more verbose basic/fundamental code by marquezc329

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