add contraction example

include/ck/tensor_operation/gpu/device/device_contraction.hpp

+#pragma once
+
+#include <iostream>
+#include <vector>
+
+#include "device_base.hpp"
+
+namespace ck {
+namespace tensor_operation {
+namespace device {
+
+template <index_t NumDimM,
+          index_t NumDimN,
+          index_t NumDimK,
+          typename AElementwiseOperation,
+          typename BElementwiseOperation,
+          typename CElementwiseOperation>
+struct DeviceContraction : public BaseOperator
+{
+    virtual std::unique_ptr<BaseArgument>
+    MakeArgumentPointer(const void* p_a,
+                        const void* p_b,
+                        void* p_c,
+                        std::vector<index_t> a_lengths,
+                        std::vector<index_t> a_strides,
+                        std::vector<index_t> b_lengths,
+                        std::vector<index_t> b_strides,
+                        std::vector<index_t> c_lengths,
+                        std::vector<index_t> c_strides,
+                        AElementwiseOperation a_element_op,
+                        BElementwiseOperation b_element_op,
+                        CElementwiseOperation c_element_op) = 0;
+
+    virtual std::unique_ptr<BaseInvoker> MakeInvokerPointer() = 0;
+};
+
+} // namespace device
+} // namespace tensor_operation
+} // namespace ck

include/ck/utility/sequence_helper.hpp

-#ifndef CK_SEQUENCE_HELPER_HPP
-#define CK_SEQUENCE_HELPER_HPP
+#pragma once
 
 #include "tuple.hpp"
 
@@ -33,4 +32,3 @@ __host__ __device__ constexpr auto to_sequence(Tuple<Number<Is>...>)
 }
 
 } // namespace ck
-#endif

include/ck/utility/tuple.hpp

-#ifndef CK_TUPLE_HPP
-#define CK_TUPLE_HPP
+#pragma once
 
 #include "integral_constant.hpp"
 #include "sequence.hpp"
@@ -173,4 +172,3 @@ constexpr Tuple<Args&...> tie(Args&... args) noexcept
 }
 
 } // namespace ck
-#endif

include/ck/utility/tuple_helper.hpp

-#ifndef CK_TUPLE_HELPER_HPP
-#define CK_TUPLE_HELPER_HPP
+#pragma once
 
 #include "functional4.hpp"
 #include "tuple.hpp"
@@ -66,4 +65,3 @@ __host__ __device__ constexpr auto transform_tuples(F f, const X& x, const Y& y,
 }
 
 } // namespace ck
-#endif