Added a HistoryArrray class

lib/pry.rb

@@ -22,6 +22,7 @@ end
 require "pry/version"
 require "pry/hooks"
 require "pry/print"
+require "pry/history_array"
 require "pry/helpers"
 require "pry/command_set"
 require "pry/commands"

lib/pry/history_array.rb

@@ -0,0 +1,105 @@
+class Pry
+  # A history array is an array to which you can only add elements. Older
+  # entries are removed progressively, so that the aray never contains more than
+  # N elements.
+  #
+  # History arrays are used by Pry to store the output of the last commands.
+  #
+  # @example
+  #   ary = Pry::HistoryArray.new 10
+  #   ary << 1 << 2 << 3
+  #   ary[0] # => 1
+  #   ary[1] # => 2
+  #   10.times { |n| ary << n }
+  #   ary[0] # => nil
+  #   ary[-1] # => 9
+  class HistoryArray
+    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)
+      if index_or_range.is_a? Integer
+        index = convert_index(index_or_range)
+
+        if size
+          end_index = index + size
+          index > @count ? nil : (index...[end_index, @count].min).map do |n|
+            @hash[n]
+          end
+        else
+          @hash[index]
+        end
+      else
+        range = convert_range(index_or_range)
+        range.begin > @count ? nil : range.map { |n| @hash[n] }
+      end
+    end
+
+    # @return [Integer] Amount of objects in the array
+    def size
+      @count
+    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
+
+    def inspect
+      to_a.inspect
+    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

test/test_history_array.rb

@@ -0,0 +1,169 @@
+require 'helper'
+
+class Pry
+  # A history array is an array to which you can only add elements. Older
+  # entries are removed progressively, so that the aray never contains more than
+  # N elements.
+  #
+  # @example
+  #   ary = Pry::HistoryArray.new 10
+  #   ary << 1 << 2 << 3
+  #   ary[0] # => 1
+  #   ary[1] # => 2
+  #   10.times { |n| ary << n }
+  #   ary[0] # => nil
+  #   ary[-1] # => 9
+  class HistoryArray
+    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)
+      if index_or_range.is_a? Integer
+        index = convert_index(index_or_range)
+
+        if size
+          end_index = index + size
+          index > @count ? nil : (index...[end_index, @count].min).map do |n|
+            @hash[n]
+          end
+        else
+          @hash[index]
+        end
+      else
+        range = convert_range(index_or_range)
+        range.begin > @count ? nil : range.map { |n| @hash[n] }
+      end
+    end
+
+    # @return [Integer] Amount of objects in the array
+    def size
+      @count
+    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
+
+    def inspect
+      to_a.inspect
+    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
+
+describe Pry::HistoryArray do
+  before do
+    @array = Pry::HistoryArray.new 10
+  end
+
+  it 'should have a maximum size specifed at creation time' do
+    @array.max_size.should == 10
+  end
+
+  it 'should be able to be added objects to' do
+    @array << 1 << 2 << 3
+    @array.size.should == 3
+    @array.to_a.should == [1, 2, 3]
+  end
+
+  it 'should be able to access single elements' do
+    @array << 1 << 2 << 3
+    @array[2].should == 3
+  end
+
+  it 'should be able to access negative indices' do
+    @array << 1 << 2 << 3
+    @array[-1].should == 3
+  end
+
+  it 'should be able to access ranges' do
+    @array << 1 << 2 << 3 << 4
+    @array[1..2].should == [2, 3]
+  end
+
+  it 'should be able to access ranges starting from a negative index' do
+    @array << 1 << 2 << 3 << 4
+    @array[-2..3].should == [3, 4]
+  end
+
+  it 'should be able to access ranges ending at a negative index' do
+    @array << 1 << 2 << 3 << 4
+    @array[2..-1].should == [3, 4]
+  end
+
+  it 'should be able to access ranges using only negative indices' do
+    @array << 1 << 2 << 3 << 4
+    @array[-2..-1].should == [3, 4]
+  end
+
+  it 'should be able to use range where end is excluded' do
+    @array << 1 << 2 << 3 << 4
+    @array[-2...-1].should == [3]
+  end
+
+  it 'should be able to access slices using a size' do
+    @array << 1 << 2 << 3 << 4
+    @array[-3, 2].should == [2, 3]
+  end
+
+  it 'should remove older entries' do
+    11.times { |n| @array << n }
+
+    @array[0].should  == nil
+    @array[1].should  == 1
+    @array[10].should == 10
+  end
+end