enumerator.c: Introduce Enumerator::ArithmeticSequence

This commit introduces new core class Enumerator::ArithmeticSequence.
Enumerator::ArithmeticSequence is a subclass of Enumerator, and
represents a number generator of an arithmetic sequence.

After this commit, Numeric#step and Range#step without blocks
returned an ArithmeticSequence object instead of an Enumerator.

This class introduces the following incompatibilities:

- You can create a zero-step ArithmeticSequence,
  and its size is not ArgumentError, but Infinity.
- You can create a negative-step ArithmeticSequence from a range.

[ruby-core:82816] [Feature #13904]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64205 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 18 insertions, 23 deletions

diff --git a/spec/ruby/core/numeric/shared/step.rb b/spec/ruby/core/numeric/shared/step.rb
index fa703b7554..f058c64a50 100644
--- a/spec/ruby/core/numeric/shared/step.rb
+++ b/spec/ruby/core/numeric/shared/step.rb
@@ -259,15 +259,15 @@ describe :numeric_step, :shared => true do
 
   describe "when no block is given" do
     it "returns an Enumerator when step is 0" do
-      1.send(@method, *@step_args.call(2, 0)).should be_an_instance_of(Enumerator)
+      1.send(@method, *@step_args.call(2, 0)).should be_an_instance_of(Enumerator::ArithmeticSequence)
     end
 
     it "returns an Enumerator when not passed a block and self > stop" do
-      1.send(@method, *@step_args.call(0, 2)).should be_an_instance_of(Enumerator)
+      1.send(@method, *@step_args.call(0, 2)).should be_an_instance_of(Enumerator::ArithmeticSequence)
     end
 
     it "returns an Enumerator when not passed a block and self < stop" do
-      1.send(@method, *@step_args.call(2, 3)).should be_an_instance_of(Enumerator)
+      1.send(@method, *@step_args.call(2, 3)).should be_an_instance_of(Enumerator::ArithmeticSequence)
     end
 
     it "returns an Enumerator that uses the given step" do
diff --git a/spec/ruby/core/numeric/step_spec.rb b/spec/ruby/core/numeric/step_spec.rb
index a932b4df73..54133f8810 100644
--- a/spec/ruby/core/numeric/step_spec.rb
+++ b/spec/ruby/core/numeric/step_spec.rb
@@ -23,23 +23,23 @@ describe "Numeric#step" do
 
     describe "when no block is given" do
       it "returns an Enumerator when step is 0" do
-        1.step(5, 0).should be_an_instance_of(Enumerator)
+        1.step(5, 0).should be_an_instance_of(Enumerator::ArithmeticSequence)
       end
 
       it "returns an Enumerator when step is 0.0" do
-        1.step(2, 0.0).should be_an_instance_of(Enumerator)
+        1.step(2, 0.0).should be_an_instance_of(Enumerator::ArithmeticSequence)
       end
 
       describe "returned Enumerator" do
         describe "size" do
           it "raises an ArgumentError when step is 0" do
             enum = 1.step(5, 0)
-            lambda { enum.size }.should raise_error(ArgumentError)
+            enum.size.should == Float::INFINITY
           end
 
           it "raises an ArgumentError when step is 0.0" do
             enum = 1.step(2, 0.0)
-            lambda { enum.size }.should raise_error(ArgumentError)
+            enum.size.should == Float::INFINITY
           end
         end
       end
diff --git a/spec/ruby/core/range/step_spec.rb b/spec/ruby/core/range/step_spec.rb
index 3d5e75b033..c364600fb0 100644
--- a/spec/ruby/core/range/step_spec.rb
+++ b/spec/ruby/core/range/step_spec.rb
@@ -5,9 +5,9 @@ describe "Range#step" do
     ScratchPad.record []
   end
 
-  it "returns an enumerator when no block is given" do
+  it "returns an arithmetic sequence when no block is given" do
     enum = (1..10).step(4)
-    enum.should be_an_instance_of(Enumerator)
+    enum.should be_an_instance_of(Enumerator::ArithmeticSequence)
     enum.to_a.should eql([1, 5, 9])
   end
 
@@ -263,7 +263,7 @@ describe "Range#step" do
   end
 
   describe "when no block is given" do
-    describe "returned Enumerator" do
+    describe "returned Enumerator::ArithmeticSequence" do
       describe "size" do
         it "raises a TypeError if step does not respond to #to_int" do
           obj = mock("Range#step non-integer")
@@ -279,19 +279,9 @@ describe "Range#step" do
           lambda { enum.size }.should raise_error(TypeError)
         end
 
-        it "raises an ArgumentError if step is 0" do
-          enum = (-1..1).step(0)
-          lambda { enum.size }.should raise_error(ArgumentError)
-        end
-
-        it "raises an ArgumentError if step is 0.0" do
-          enum = (-1..1).step(0.0)
-          lambda { enum.size }.should raise_error(ArgumentError)
-        end
-
-        it "raises an ArgumentError if step is negative" do
-          enum = (-1..1).step(-2)
-          lambda {  enum.size }.should raise_error(ArgumentError)
+        it "returns Float::INFINITY for zero step" do
+          (-1..1).step(0).size.should == Float::INFINITY
+          (-1..1).step(0.0).size.should == Float::INFINITY
         end
 
         it "returns the ceil of range size divided by the number of steps" do
@@ -307,6 +297,11 @@ describe "Range#step" do
           (-5...5).step(2).size.should == 5
         end
 
+        it "returns the ceil of range size divided by the number of steps even if step is negative" do
+          (-1..1).step(-1).size.should == 0
+          (1..-1).step(-1).size.should == 3
+        end
+
         it "returns the correct number of steps when one of the arguments is a float" do
           (-1..1.0).step(0.5).size.should == 5
           (-1.0...1.0).step(0.5).size.should == 4