Allow operator methods to be memoized

Memoizing operators will raise a syntax error due to the operator symbols
being injected into the eval'd code. We can allow operator memoization by
using some mangled names instead. To (hopefully) avoid clashing with any
existing method names, we've added some underscores to the names and
upper-cased them.

lib/memoist.rb

@@ -3,6 +3,34 @@
 require 'memoist/version'
 
 module Memoist
+  OPERATOR_METHOD_NAMES = {
+    '[]'  =>  '__ELEMENT_ACCESS_OP__',
+    '[]=' =>  '__ELEMENT_ASSIGNMENT_OP__',
+    '**'  =>  '__EXPOENTIATION_OP__',
+    '!'   =>  '__NEGATION_BANG_OP__',
+    '~'   =>  '__COMPLEMENT_OP__',
+    '+@'  =>  '__UNARY_PLUS_OP__',
+    '-@'  =>  '__UNARY_MINUS_OP__',
+    '*'   =>  '__MULTIPLICATION_OP__',
+    '/'   =>  '__DIVISION_OP__',
+    '%'   =>  '__MODULO_OP__',
+    '+'   =>  '__PLUS_OP__',
+    '-'   =>  '__MINUS_OP__',
+    '>>'  =>  '__BITWISE_SHIFT_RIGHT_OP__',
+    '<<'  =>  '__BITWISE_SHIFT_LEFT_OP__',
+    '&'   =>  '__BITWISE_AND_OP__',
+    '^'   =>  '__BITWISE_EXCLUSIVE_OR_OP__',
+    '|'   =>  '__BITWISE_OR_OP__',
+    '<='  =>  '__LTE_OP__',
+    '<'   =>  '__LT_OP__',
+    '>'   =>  '__GT_OP__',
+    '>='  =>  '__GTE_OP__',
+    '<=>' =>  '__SPACESHIP_OP__',
+    '=='  =>  '__EQUALITY_OP__',
+    '===' =>  '__TRIPLE_EQUALITY_OP__',
+    '=~'  =>  '__MATCH_OP__',
+  }.freeze
+
   def self.extended(extender)
     Memoist.memoist_eval(extender) do
       unless singleton_class.method_defined?(:memoized_methods)
@@ -13,12 +41,16 @@ def self.memoized_methods
     end
   end
 
+  def self.method_name_for(method_name)
+    OPERATOR_METHOD_NAMES.fetch(method_name.to_s, method_name)
+  end
+
   def self.memoized_ivar_for(method_name, identifier = nil)
-    "@#{memoized_prefix(identifier)}_#{escape_punctuation(method_name)}"
+    "@#{memoized_prefix(identifier)}_#{escape_punctuation(method_name_for(method_name))}"
   end
 
   def self.unmemoized_method_for(method_name, identifier = nil)
-    "#{unmemoized_prefix(identifier)}_#{method_name}".to_sym
+    "#{unmemoized_prefix(identifier)}_#{method_name_for(method_name)}".to_sym
   end
 
   def self.memoized_prefix(identifier = nil)

test/memoist_test.rb

@@ -130,6 +130,40 @@ def name
     end
   end
 
+  class OperatorMethods
+    extend Memoist
+
+    OPERATORS = %w{
+      [] []=
+      **
+      ! ~ +@ -@
+      * / %
+      + -
+      >> <<
+      &
+      ^ |
+      <= < > >=
+      <=>
+      == === =~
+    }.freeze
+
+    attr_reader :counter
+
+    def initialize
+      @counter = CallCounter.new
+    end
+
+    OPERATORS.each do |operator|
+      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
+        def #{operator}(other)
+          @counter.call(#{operator.inspect})
+          'foo'
+        end
+        memoize :#{operator}
+      EOS
+    end
+  end
+
   module Rates
     extend Memoist
 
@@ -547,4 +581,16 @@ def test_private_method_memoization
     assert_equal 'Yes', person.send(:is_developer?)
     assert_equal 1, person.is_developer_calls
   end
+
+  def test_operator_method_names
+    operator_methods = OperatorMethods.new
+
+    OperatorMethods::OPERATORS.each do |operator|
+      3.times { operator_methods.send(operator, 'bar') }
+
+      assert_equal 1, operator_methods.counter.count(operator)
+      assert_equal 'foo', operator_methods.send(operator, 'bar', :reload)
+      assert_equal 2, operator_methods.counter.count(operator)
+    end
+  end
 end