1 files changed, 117 insertions, 0 deletions
diff --git a/lib/pry/ring.rb b/lib/pry/ring.rb
new file mode 100644
index 00000000..4980cb3c
--- /dev/null
+++ b/lib/pry/ring.rb
@@ -0,0 +1,117 @@
+class Pry
+  # A ring is an array to which you can only add elements. Older entries are
+  # removed progressively, so that the array never contains more than N
+  # elements.
+  #
+  # Rings are used by Pry to store the output of the last commands.
+  #
+  # @example
+  #   ring = Pry::Ring.new(10)
+  #   ring << 1 << 2 << 3
+  #   ring[0] # => 1
+  #   ring[1] # => 2
+  #   10.times { |n| ring << n }
+  #   ring[0] # => nil
+  #   ring[-1] # => 9
+  class Ring
+    include Enumerable
+
+    # @param [Integer] size Maximum amount of objects in the array
+    def initialize(size)
+      @max_size = size
+
+      @hash  = {}
+      @count = 0
+    end
+
+    # Pushes an object at the end of the array
+    # @param [Object] value Object to be added
+    def <<(value)
+      @hash[@count] = value
+
+      if @hash.size > max_size
+        @hash.delete(@count - max_size)
+      end
+
+      @count += 1
+
+      self
+    end
+
+    # @overload [](index)
+    #   @param [Integer] index Index of the item to access.
+    #   @return [Object, nil] Item at that index or nil if it has been removed.
+    # @overload [](index, size)
+    #   @param [Integer] index Index of the first item to access.
+    #   @param [Integer] size Amount of items to access
+    #   @return [Array, nil] The selected items. Nil if index is greater than
+    #     the size of the array.
+    # @overload [](range)
+    #   @param [Range<Integer>] range Range of indices to access.
+    #   @return [Array, nil] The selected items. Nil if index is greater than
+    #     the size of the array.
+    def [](index_or_range, size = nil)
+      unless index_or_range.is_a?(Integer)
+        range = convert_range(index_or_range)
+        return range.begin > @count ? nil : range.map { |n| @hash[n] }
+      end
+
+      index = convert_index(index_or_range)
+      return @hash[index] unless size
+      return if index > @count
+
+      end_index = index + size
+      (index...[end_index, @count].min).map { |n| @hash[n] }
+    end
+
+    # @return [Integer] Amount of objects in the array
+    def size
+      @count
+    end
+    alias count size
+    alias length size
+
+    def empty?
+      size == 0
+    end
+
+    def each
+      ((@count - size)...@count).each do |n|
+        yield @hash[n]
+      end
+    end
+
+    def to_a
+      ((@count - size)...@count).map { |n| @hash[n] }
+    end
+
+    # @return [Hash] copy of the internal @hash history
+    def to_h
+      @hash.dup
+    end
+
+    def pop!
+      @hash.delete @count - 1
+      @count -= 1
+    end
+
+    def inspect
+      "#<#{self.class} size=#{size} first=#{@count - size} max_size=#{max_size}>"
+    end
+
+    # @return [Integer] Maximum amount of objects in the array
+    attr_reader :max_size
+
+    private
+    def convert_index(n)
+      n >= 0 ? n : @count + n
+    end
+
+    def convert_range(range)
+      end_index = convert_index(range.end)
+      end_index += 1 unless range.exclude_end?
+
+      Range.new(convert_index(range.begin), [end_index, @count].min, true)
+    end
+  end
+end