module Enumerable(T)
  def count_each
    count_map = {} of T => Int32
    each do |other|
      count_map[other] = (count_map[other]? || 0) + 1
    end
    return count_map
  end
end

class Rectangle
  def initialize(@x : Int32, @y : Int32, @width : Int32, @height : Int32)
  end

  def each_coord(&block)
    (@x...(@x + @width)).each do |x|
      (@y...(@y + @height)).each do |y|
        yield x, y
      end
    end
  end
end

class String
  def select(&block)
    String.build do |s|
      each_char do |c|
        s << c if yield c
      end
    end
  end

  def select!(&block)
    i = 0
    s = size
    while i < s
      if yield [i]
        i += 1
      else
        s -= 1
      end
    end
  end
end