Fix `Rational#==(Complex)`

Consider a Numreic class like `Complex` that does not have `<=>` but `==`
works (`0i == 0r` is `true`).

mrbgems/mruby-rational/mrblib/rational.rb

@@ -62,6 +62,19 @@ class Rational < Numeric
       nil
     end
   end
+
+  def ==(rhs)
+    if rhs.is_a?(Integral)
+      return numerator == rhs if denominator == 1
+      rhs = Rational(rhs)
+    end
+
+    if rhs.is_a?(Rational)
+      numerator * rhs.denominator == denominator * rhs.numerator
+    else
+      rhs == self
+    end
+  end
 end
 
 class Numeric

mrbgems/mruby-rational/test/rational.rb

+class UserDefinedNumeric < Numeric
+  def initialize(n)
+    @n = n
+  end
+
+  def <=>(rhs)
+    return nil unless rhs.respond_to?(:to_i)
+    rhs = rhs.to_i
+    rhs < 0 ? nil : @n <=> rhs
+  end
+
+  def inspect
+    "#{self.class}(#{@n})"
+  end
+end
+
+class ComplexLikeNumeric < UserDefinedNumeric
+  def ==(rhs)
+    @n == 0 && rhs == 0
+  end
+
+  undef <=>
+end
+
 def assert_rational(exp, real)
   assert_float exp.numerator,   real.numerator
   assert_float exp.denominator, real.denominator
@@ -17,7 +41,7 @@ def assert_cmp(exp, o1, o2)
   if exp == (o1 <=> o2)
     pass
   else
-    flunk "", "    Expected #{o1.inspect} <=> #{o2.inspect} to be #{exp}"
+    flunk "", "    Expected #{o1.inspect} <=> #{o2.inspect} to be #{exp}."
   end
 end
 
@@ -106,6 +130,13 @@ assert 'Rational#==, Rational#!=' do
   assert_equal_rational(false, Rational(2,1), 1r)
   assert_equal_rational(false, Rational(1), nil)
   assert_equal_rational(false, Rational(1), '')
+  assert_equal_rational(true, 0r, UserDefinedNumeric.new(0))
+  assert_equal_rational(true, 1r, UserDefinedNumeric.new(1))
+  assert_equal_rational(false, 1r, UserDefinedNumeric.new(2))
+  assert_equal_rational(false, -1r, UserDefinedNumeric.new(-1))
+  assert_equal_rational(true, 0r, ComplexLikeNumeric.new(0))
+  assert_equal_rational(false, 1r, ComplexLikeNumeric.new(1))
+  assert_equal_rational(false, 1r, ComplexLikeNumeric.new(2))
 end
 
 assert 'Fixnum#==(Rational), Fixnum#!=(Rational)' do
@@ -123,21 +154,6 @@ assert 'Float#==(Rational), Float#!=(Rational)' do
 end
 
 assert 'Rational#<=>' do
-  num = Class.new(Numeric) do
-    def initialize(n)
-      @n = n
-    end
-
-    def <=>(rhs)
-      rhs = rhs.to_i
-      rhs < 0 ? nil : @n <=> rhs
-    end
-
-    def inspect
-      "num(#{@n})"
-    end
-  end
-
   assert_cmp(-1, Rational(-1), Rational(0))
   assert_cmp(0, Rational(0), Rational(0))
   assert_cmp(1, Rational(1), Rational(0))
@@ -158,10 +174,12 @@ assert 'Rational#<=>' do
   assert_cmp(-1, Rational(1,2), Rational(2,3))
   assert_cmp(-1, Rational(1,2), Rational(2,3))
   assert_cmp(nil, 3r, "3")
-  assert_cmp(1, 3r, num.new(2))
-  assert_cmp(0, 3r, num.new(3))
-  assert_cmp(-1, 3r, num.new(4))
-  assert_cmp(nil, Rational(-3), num.new(5))
+  assert_cmp(1, 3r, UserDefinedNumeric.new(2))
+  assert_cmp(0, 3r, UserDefinedNumeric.new(3))
+  assert_cmp(-1, 3r, UserDefinedNumeric.new(4))
+  assert_cmp(nil, Rational(-3), UserDefinedNumeric.new(5))
+  assert_raise(NoMethodError) { 0r <=> ComplexLikeNumeric.new(0) }
+  assert_raise(NoMethodError) { 1r <=> ComplexLikeNumeric.new(2) }
 end
 
 assert 'Fixnum#<=>(Rational)' do