String#rotate

lib/core/facets/string/rotate.rb

@@ -0,0 +1,26 @@
+class String
+
+  # Rotate string to the left with count.
+  # Specifying negative number indicates rotation to the right.
+  #
+  #   'abcdefgh'.rotate(2)  #=> 'cdefghab'
+  #   'abcdefgh'.rotate(-2) #=> 'ghabcdef'
+  #
+  # CREDIT: T. Yamada
+
+  def rotate(count=1)
+    count+=self.length if count<0
+    self.slice(count,self.length-count)+self.slice(0,count)
+  end
+
+  # Destructive version of String#rotate
+  #
+  #   s='abcdefgh'
+  #   s.rotate!(2)
+  #   s.should eq 'cdefghab'
+  #
+  # CREDIT: T. Yamada
+
+  def rotate!(count=1) self.replace(self.rotate(count)) end
+
+end

test/core/string/test_rotate.rb

@@ -0,0 +1,31 @@
+covers 'facets/string/rotate'
+
+test_case String do
+
+  method :rotate do
+
+    test 'rotates left' do
+      'abcdefgh'.rotate(2).assert == 'cdefghab'
+    end
+    test 'rotates right' do
+      'abcdefgh'.rotate(-2).assert == 'ghabcdef'
+    end
+
+  end
+
+  method :rotate! do
+
+    test 'rotates left' do
+      s='abcdefgh'
+      s.rotate!(2)
+      s.assert == 'cdefghab'
+    end
+    test 'rotates right' do
+      s='abcdefgh'
+      s.rotate!(-2)
+      s.assert == 'ghabcdef'
+    end
+
+  end
+
+end