[Crystal] Descending range

range-descending.cr

struct Range

  # Iterates over the elements of this range, passing each in turn to the block.
  #
  # ```
  # (10..15).each { |n| print n, ' ' }
  # # prints: 10 11 12 13 14 15
  # ```
  def each : Nil
    {% if B == Nil %}
      {% raise "Can't each beginless range" %}
    {% end %}

    current = @begin
    if current.nil?
      raise ArgumentError.new("Can't each beginless range")
    end

    # TODO: This typeof and the macro interpolations are a workaround until #9324 is fixed.
    typeof(yield current)

    {% if E == Nil %}
      while true
        {{ "yield current".id }}
        current = current.succ
      end
    {% else %}
      end_value = @end
      if end_value.nil?
        while true
          {{ "yield current".id }}
          current = current.succ
        end
      else
        if current < end_value
          while current < end_value
            {{ "yield current".id }}
            current = current.succ
          end
        else
          while current > end_value
            {{ "yield current".id }}
            current = current.pred
          end
        end
        {{ "yield current".id }} if !@exclusive && (current <=> end_value).zero?
      end
    {% end %}
  end
  
  def empty?
    @begin == @end && [email protected]? && @exclusive
  end

  def direction
    if @begin == @end && [email protected]?
      0
    elsif (from = @begin) && (to = @end)
      (to <=> from).sign
    else
      1
    end
  end

  # Returns `true` if this range includes the given *value*.
  #
  # ```
  # (1..10).includes?(4)  # => true
  # (1..10).includes?(10) # => true
  # (1..10).includes?(11) # => false
  #
  # (1...10).includes?(9)  # => true
  # (1...10).includes?(10) # => false
  # ```
  def includes?(value)
    begin_value = @begin
    end_value = @end

    direction = self.direction

    # begin passes
    ((begin_value.nil? || (value <=> begin_value).sign != -direction) &&
      # end passes
      (end_value.nil? ||
        (value <=> end_value).sign.in?(@exclusive ? {-direction} : {-direction, 0})))
  end

  private class ItemIterator(B, E)
    def next
      return stop if @reached_end

      end_value = @range.end

      if end_value.nil? || @current != end_value
        value = @current
        if @range.direction == -1
          @current = @current.pred
        else
          @current = @current.succ
        end
        value
      else
        @reached_end = true

        if [email protected]_end? && @current == end_value
          @current
        else
          stop
        end
      end
    end
  end
end