Functional additions to ruby "array"

arr.rb

# Threw together these two functions to demonstrate adding some immutable modification
# functions to Ruby's Array class.  "update" takes a hash of indices to values and
# returns a new array with the appropriate indices replaced by the supplied values.
# "modify" takes a list of indices and runs the block on those indices that match;
# like a version of "map" where you can specify the indices.

# Maybe you can already do this in Ruby, but I couldn't see anything in the docs so
# here's my hacky little monkey patch...

class Array
  def update(replacements)                                                                                                                              
    each_with_index.map{ |x, i| replacements.include?(i) ? replacements[i] : x }.to_a                                                                   
  end
  
  def modify(indices)
    each_with_index.map{ |x, i| indices.include?(i) ? yield(x) : x }.to_a
  end
end

# [1, 2, 3, 4].update(2 => 'a')                                                                                                                           
# => [1, 2, "a", 4] 

# [1, 2, 3, 4].modify [2] { |x| x = x + 1 }
# => [1, 2, 4, 4]