[SOLVED] join enumerable to produce string in Ruby

join enumerable to produce string in Ruby

Ruby arrays have the #join method that produces a string by joining the elements of the array, adding an optional separator.

Other enumerables such as ranges don't have the same method.

You could emulate the behaviour using #inject, e.g.

('a'..'z').inject('') do |acc, s| 
  if acc.empty?
    s
  else
    acc << ' some separator ' << s.to_s  
  end
end

Is there a better way to join enumerables? Was #join omitted for a particular reason?

EDIT:

One thing I would be concerned about would be copying a massive enumerable to an array. Of course that's seldom a use case, but still. For instance:

(1 .. 1_000_000_000_000_000).to_a.join

Therefore I'm particularly interested in solutions that don't require generating an array with all the values as an intermediate step.

Solution

The code within your question is already as optimal as it gets, but it's possible to remove the condition inside your block:

e = ('a'..'z').to_enum

joined_string = e.reduce { |acc, str| acc << ' some separator ' << str }.to_s

Without passing an argument to #reduce, the first time the block gets called, acc and str would represent the first two elements of the enumerable. The additional .to_s at the end is to ensure that an empty string is returned if the enumerable is empty.