Fix parallel assignment offense.

lib/rspec/support/version_checker.rb:8:9: C: Do not use parallel assignment.
        @library_name, @library_version = library_name, library_version
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Author: cupakromer

benchmarks/parallel_vs_sequential_assignment.rb

@@ -0,0 +1,291 @@
+require 'benchmark'
+
+class SequentialWidget
+  def initialize
+    a = 1
+    b = 2
+  end
+end
+
+def sequential_initialize_assignment
+  SequentialWidget.new
+end
+
+class ParallelWidget
+  def initialize
+    a, b = 1, 2
+  end
+end
+
+def parallel_initialize_assignment
+  ParallelWidget.new
+end
+
+def sequential_local_assignment
+  a = 1
+  b = 2
+  # Simulate that the assignment is not the method return value but do
+  # not add more work to this method
+  :noop
+end
+
+def parallel_local_assignment
+  a, b = 1, 2
+  # Simulate that the assignment is not the method return value but do
+  # not add more work to this method
+  :noop
+end
+
+def sequential_block_assignment
+  a = nil
+  b = nil
+  (1..10).each do |x|
+    a = b
+    b = x
+  end
+  # Simulate that the assignment is not the method return value but do
+  # not add more work to this method
+  :noop
+end
+
+def parallel_block_assignment
+  a = nil
+  b = nil
+  (1..10).each do |x|
+    a, b = b, x
+  end
+  # Simulate that the assignment is not the method return value but do
+  # not add more work to this method
+  :noop
+end
+
+
+puts
+puts "Ruby #{RUBY_VERSION}"
+puts
+begin
+  require 'benchmark/ips'
+
+  Benchmark.ips do |x|
+    x.report('Parallel Local Assignment       ') do
+      parallel_local_assignment
+    end
+
+    x.report('Sequential Local Assignment     ') do
+      sequential_local_assignment
+    end
+
+    x.compare!
+  end
+
+  Benchmark.ips do |x|
+    x.report('Parallel Initialize Assignment  ') do
+      parallel_initialize_assignment
+    end
+
+    x.report('Sequential Initialize Assignment') do
+      sequential_initialize_assignment
+    end
+
+    x.compare!
+  end
+
+  Benchmark.ips do |x|
+    x.report('Parallel Block Assignment       ') do
+      parallel_block_assignment
+    end
+
+    x.report('Sequential Block Assignment     ') do
+      sequential_block_assignment
+    end
+
+    x.compare!
+  end
+
+rescue LoadError
+
+  # We are on an older Ruby which does not support benchmark/ips
+  n = 100_000
+
+  puts "#{n} times"
+
+  Benchmark.benchmark do |bm|
+    puts
+    puts "Parallel Local Assignment"
+    3.times { bm.report { n.times { parallel_local_assignment } } }
+
+    puts
+    puts "Sequential Local Assignment"
+    3.times { bm.report { n.times { sequential_local_assignment } } }
+  end
+
+  Benchmark.benchmark do |bm|
+    puts
+    puts "Parallel Initialize Assignment"
+    3.times { bm.report { n.times { parallel_initialize_assignment } } }
+
+    puts
+    puts "Sequential Initialize Assignment"
+    3.times { bm.report { n.times { sequential_initialize_assignment } } }
+  end
+
+  Benchmark.benchmark do |bm|
+    puts
+    puts "Parallel Block Assignment"
+    3.times { bm.report { n.times { parallel_block_assignment } } }
+
+    puts
+    puts "Sequential Block Assignment"
+    3.times { bm.report { n.times { sequential_block_assignment } } }
+  end
+end
+
+__END__
+
+This is a complicated benchmark. Sequential assignment is always faster on Ruby
+1.8.7, REE, and JRuby. However, on Ruby 1.9 and 2.x it depends where the
+assignment is used - and how many assignments are made.
+
+On Ruby 1.9 and 2.x the assignment of two variable is essentially equally fast
+for parallel and sequent. However, as the number of assignments go up parallel
+assignment becomes increasingly faster. However, it depends on the context of
+that assignment. If the assignment LOC is also an _**implicit**_ return, thus
+if it's the last line of a method or a block (this is true for blocks even when
+the block return value is ignored), then Ruby will return all variable values
+as an array! This array creation is slow and will make sequential assignment
+faster, as the incidental array is not created.
+
+Given that there is little benefit for the common case of parallel assignment
+for two varaibles, and it's less common to see parallel assignment for three
+variables, and extremely rare for any number greater we should default to
+sequential assignment. [Aaron Kromer]
+
+Ruby 1.8.7
+
+100000 times
+
+Parallel Local Assignment
+  0.080000   0.000000   0.080000 (  0.079573)
+  0.060000   0.000000   0.060000 (  0.067334)
+  0.060000   0.000000   0.060000 (  0.059873)
+
+Sequential Local Assignment
+  0.030000   0.000000   0.030000 (  0.030429)
+  0.030000   0.010000   0.040000 (  0.030158)
+  0.020000   0.000000   0.020000 (  0.023209)
+
+Parallel Initialize Assignment
+  0.090000   0.000000   0.090000 (  0.085544)
+  0.080000   0.000000   0.080000 (  0.084318)
+  0.080000   0.000000   0.080000 (  0.085762)
+
+Sequential Initialize Assignment
+  0.050000   0.000000   0.050000 (  0.048160)
+  0.050000   0.000000   0.050000 (  0.049463)
+  0.050000   0.000000   0.050000 (  0.051358)
+
+Parallel Block Assignment
+  0.460000   0.000000   0.460000 (  0.469698)
+  0.460000   0.000000   0.460000 (  0.457632)
+  0.450000   0.010000   0.460000 (  0.462481)
+
+Sequential Block Assignment
+  0.230000   0.000000   0.230000 (  0.240600)
+  0.230000   0.000000   0.230000 (  0.245943)
+  0.230000   0.000000   0.230000 (  0.230579)
+
+
+Ruby 1.9.3
+
+Calculating -------------------------------------
+Parallel Local Assignment
+                        89.220k i/100ms
+Sequential Local Assignment
+                        91.383k i/100ms
+-------------------------------------------------
+Parallel Local Assignment
+                          5.075M (± 8.8%) i/s -     25.249M
+Sequential Local Assignment
+                          5.029M (±12.1%) i/s -     24.673M
+
+Comparison:
+Parallel Local Assignment       :  5074905.9 i/s
+Sequential Local Assignment     :  5028923.8 i/s - 1.01x slower
+
+Calculating -------------------------------------
+Parallel Initialize Assignment
+                        61.930k i/100ms
+Sequential Initialize Assignment
+                        66.286k i/100ms
+-------------------------------------------------
+Parallel Initialize Assignment
+                          1.943M (± 5.3%) i/s -      9.723M
+Sequential Initialize Assignment
+                          2.124M (± 9.8%) i/s -     10.606M
+
+Comparison:
+Sequential Initialize Assignment:  2123826.3 i/s
+Parallel Initialize Assignment  :  1943162.0 i/s - 1.09x slower
+
+Calculating -------------------------------------
+Parallel Block Assignment
+                        30.497k i/100ms
+Sequential Block Assignment
+                        36.997k i/100ms
+-------------------------------------------------
+Parallel Block Assignment
+                        579.905k (± 7.7%) i/s -      2.897M
+Sequential Block Assignment
+                        896.073k (± 7.7%) i/s -      4.477M
+
+Comparison:
+Sequential Block Assignment     :   896072.9 i/s
+Parallel Block Assignment       :   579904.9 i/s - 1.55x slower
+
+
+Ruby 2.2.2
+
+Calculating -------------------------------------
+Parallel Local Assignment
+                        83.984k i/100ms
+Sequential Local Assignment
+                        86.309k i/100ms
+-------------------------------------------------
+Parallel Local Assignment
+                          5.602M (±12.0%) i/s -     27.043M
+Sequential Local Assignment
+                          5.482M (± 8.0%) i/s -     27.274M
+
+Comparison:
+Parallel Local Assignment       :  5602180.9 i/s
+Sequential Local Assignment     :  5482370.9 i/s - 1.02x slower
+
+Calculating -------------------------------------
+Parallel Initialize Assignment
+                        64.000k i/100ms
+Sequential Initialize Assignment
+                        67.066k i/100ms
+-------------------------------------------------
+Parallel Initialize Assignment
+                          2.044M (± 5.5%) i/s -     10.240M
+Sequential Initialize Assignment
+                          2.488M (± 6.3%) i/s -     12.407M
+
+Comparison:
+Sequential Initialize Assignment:  2487575.1 i/s
+Parallel Initialize Assignment  :  2044428.9 i/s - 1.22x slower
+
+Calculating -------------------------------------
+Parallel Block Assignment
+                        34.362k i/100ms
+Sequential Block Assignment
+                        45.586k i/100ms
+-------------------------------------------------
+Parallel Block Assignment
+                        593.794k (± 4.5%) i/s -      2.989M
+Sequential Block Assignment
+                        886.536k (±12.3%) i/s -      4.331M
+
+Comparison:
+Sequential Block Assignment     :   886535.9 i/s
+Parallel Block Assignment       :   593793.6 i/s - 1.49x slower