Can't all or most cases of `each` be replaced with `map`?

Question

The difference between Enumerable#each and Enumerable#map is whether it returns the receiver or the mapped result. Getting back to the receiver is trivial and you usually do not need to continue a method chain after each like each{...}.another_method (I probably have not seen such case. Even if you want to get back to the receiver, you can do that with tap). So I think all or most cases where Enumerable#each is used can be replaced by Enumerable#map. Am I wrong? If I am right, what is the purpose of each? Is map slower than each?

Edit: I know that there is a common practice to use each when you are not interested in the return value. I am not interested in whether such practice exists, but am interested in whether such practice makes sense other than from the point of view of convention.

Answer 1

The difference between map and each is more important than whether one returns a new array and the other doesn't. The important difference is in how they communicate your intent.

When you use each, your code says "I'm doing something for each element." When you use map, your code says "I'm creating a new array by transforming each element."

So while you could use map in place of each, performance notwithstanding, the code would now be lying about its intent to anyone reading it.

Answer 2

The choice between map or each should be decided by the desired end result: a new array or no new array. The result of map can be huge and/or silly:

p ("aaaa".."zzzz").map{|word| puts word} #huge and useless array of nil's