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rubyenumerable

Reversing enumerable in Ruby

I'm trying to reverse Enumerable (like Array) without using reverse method, but using reverse_each iterator.

I hoped, that following code is enough:

p [1,2,3].reverse_each {|v| v }

however the block doesn't return array in reversed orded. Of course I could write

[1,2,3].reverse_each {|v| p v }

but I'd like to collect items in the first way. What is the source if this behaviour and how should I write my expression to fulfill requirement?

Solution

  • From 1.8.7, Enumerable#each_* methods return an enumerator when no block is provided, so those originally imperative methods can now be used in pure expressions.

    So, if you want to collect items, use Enumerable#map on that enumerator:

    reversed_values = [1, 2, 3].reverse_each.map { |x| 2*x }
#=> [6, 4, 2]