Rename HistoryArray to Ring

`HistoryArray` is a very specific name and it doesn't tell the reader what
it *really* means unless you read its code or the docs of the class.

On the other hand, `Ring` is a [very well-known term][1], which means exactly
what `HistoryArray` does. The alias name for it is circular buffer. I chose
`Ring` because it is shorter and used by Golang, so I expect programmers to
be familiar with `Ring`.

[1]: https://en.wikipedia.org/wiki/Circular_buffer

lib/pry.rb

@@ -144,7 +144,7 @@ require 'pathname'
 require 'pry/version'
 require 'pry/repl'
 require 'pry/code'
-require 'pry/history_array'
+require 'pry/ring'
 require 'pry/helpers'
 require 'pry/code_object'
 require 'pry/method'

lib/pry/pry_instance.rb

@@ -72,8 +72,8 @@ class Pry
     @config = Pry::Config.new
     config.merge!(options)
     push_prompt(config.prompt)
-    @input_array  = Pry::HistoryArray.new config.memory_size
-    @output_array = Pry::HistoryArray.new config.memory_size
+    @input_array  = Pry::Ring.new(config.memory_size)
+    @output_array = Pry::Ring.new(config.memory_size)
     @custom_completions = config.command_completions
     set_last_result nil
     @input_array << nil
@@ -177,8 +177,8 @@ class Pry
 
   undef :memory_size= if method_defined? :memory_size=
   def memory_size=(size)
-    @input_array  = Pry::HistoryArray.new(size)
-    @output_array = Pry::HistoryArray.new(size)
+    @input_array  = Pry::Ring.new(size)
+    @output_array = Pry::Ring.new(size)
   end
 
   # Inject all the sticky locals into the current binding.

lib/pry/ring.rb

@@ -1,19 +1,19 @@
 class Pry
-  # A history array 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.
+  # 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.
   #
-  # History arrays are used by Pry to store the output of the last commands.
+  # Rings 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
+  #   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

spec/pry_spec.rb

@@ -273,7 +273,7 @@ describe Pry do
           t.eval "42"
           res = t.eval "_out_"
 
-          expect(res).to be_a_kind_of Pry::HistoryArray
+          expect(res).to be_a_kind_of(Pry::Ring)
           expect(res[1..2]).to eq [:foo, 42]
         end
 
@@ -283,7 +283,7 @@ describe Pry do
           t.eval "42"
           res = t.eval "_in_"
 
-          expect(res).to be_a_kind_of Pry::HistoryArray
+          expect(res).to be_a_kind_of(Pry::Ring)
           expect(res[1..2]).to eq [":foo\n", "42\n"]
         end
 

spec/ring_spec.rb

@@ -1,13 +1,13 @@
 require_relative 'helper'
 
-describe Pry::HistoryArray do
+describe Pry::Ring do
   before do
-    @array = Pry::HistoryArray.new 10
-    @populated = @array.dup << 1 << 2 << 3 << 4
+    @ring = Pry::Ring.new(10)
+    @populated = @ring.dup << 1 << 2 << 3 << 4
   end
 
   it 'should have a maximum size specifed at creation time' do
-    expect(@array.max_size).to eq 10
+    expect(@ring.max_size).to eq 10
   end
 
   it 'should be able to be added objects to' do
@@ -48,16 +48,16 @@ describe Pry::HistoryArray do
   end
 
   it 'should remove older entries' do
-    11.times { |n| @array << n }
+    11.times { |n| @ring << n }
 
-    expect(@array[0]).to  eq nil
-    expect(@array[1]).to  eq 1
-    expect(@array[10]).to eq 10
+    expect(@ring[0]).to  eq nil
+    expect(@ring[1]).to  eq 1
+    expect(@ring[10]).to eq 10
   end
 
   it 'should not be larger than specified maximum size' do
-    12.times { |n| @array << n }
-    expect(@array.entries.compact.size).to eq 10
+    12.times { |n| @ring << n }
+    expect(@ring.entries.compact.size).to eq 10
   end
 
   it 'should pop!' do