add at method to SortedArray

lib/sorted_containers/sorted_array.rb

@@ -213,6 +213,19 @@ def add(value)
 
     # rubocop:enable Metrics/MethodLength
 
+    # Returns the element at +Integer+ offset +index+; does not modify +self+.
+    # If +index+ is negative, counts from the end of +self+.
+    # Returns +nil+ if the +index+ is out of range.
+    # Will raise +TypeError+ if the +index+ is not an +Integer+.
+    #
+    # @param index [Integer] The index of the value to retrieve.
+    # @return [Object] The value at the specified index.
+    def at(index)
+      raise TypeError, "no implicit conversion of #{index.class} into Integer" unless index.is_a?(Integer)
+
+      self[index.to_i]
+    end
+
     # Returns a string representation of the sorted array.
     #
     # @return [String] A string representation of the sorted array.

spec/sorted_array_spec.rb

@@ -321,6 +321,28 @@
     end
   end
 
+  describe "at" do
+    it "should return the value at the given index" do
+      array = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect(array.at(2)).to eq(3)
+    end
+
+    it "should handle negative indices" do
+      array = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect(array.at(-1)).to eq(5)
+    end
+
+    it "should return nil if negative index is out of range" do
+      array = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect(array.at(-6)).to be_nil
+    end
+
+    it "should raise exception when index is a range" do
+      array = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect { array.at(1..3) }.to raise_error(TypeError)
+    end
+  end
+
   describe "load_factor" do
     it "should set the load factor to the provided value" do
       array = SortedContainers::SortedArray.new([], load_factor: 100)