Replace some assertions with concepts

include/etl/index.hpp

@@ -93,10 +93,8 @@ constexpr size_t fast_index(size_t i) noexcept(assert_nothrow) {
  * \param j The index of the second dimension to access
  * \return The flat position of (i,j)
  */
-template <typename T>
+template <etl_2d T>
 constexpr size_t fast_index(size_t i, size_t j) noexcept(assert_nothrow) {
-    static_assert(is_2d<T>, "Invalid number of dimensions for fast_index");
-
     if constexpr (decay_traits<T>::storage_order == order::RowMajor) {
         cpp_assert(i < decay_traits<T>::template dim<0>(), "Out of bounds");
         cpp_assert(j < decay_traits<T>::template dim<1>(), "Out of bounds");
@@ -117,10 +115,8 @@ constexpr size_t fast_index(size_t i, size_t j) noexcept(assert_nothrow) {
  * \param k The index of the third dimension to access
  * \return The flat position of (i,j,k)
  */
-template <typename T>
+template <etl_3d T>
 constexpr size_t fast_index(size_t i, size_t j, size_t k) noexcept(assert_nothrow) {
-    static_assert(is_3d<T>, "Invalid number of dimensions for fast_index");
-
     if constexpr (decay_traits<T>::storage_order == order::RowMajor) {
         cpp_assert(i < decay_traits<T>::template dim<0>(), "Out of bounds");
         cpp_assert(j < decay_traits<T>::template dim<1>(), "Out of bounds");
@@ -144,10 +140,8 @@ constexpr size_t fast_index(size_t i, size_t j, size_t k) noexcept(assert_nothro
  * \param l The index of the fourth dimension to access
  * \return The flat position of (i,j,k,l)
  */
-template <typename T>
+template <etl_4d T>
 constexpr size_t fast_index(size_t i, size_t j, size_t k, size_t l) noexcept(assert_nothrow) {
-    static_assert(is_4d<T>, "Invalid number of dimensions for fast_index");
-
     if constexpr (decay_traits<T>::storage_order == order::RowMajor) {
         cpp_assert(i < decay_traits<T>::template dim<0>(), "Out of bounds");
         cpp_assert(j < decay_traits<T>::template dim<1>(), "Out of bounds");

include/etl/op/flip_transformers.hpp

@@ -16,15 +16,13 @@ namespace etl {
  *
  * \tparam T The type on which the transformer is applied
  */
-template <typename T>
+template <etl_2d T>
 struct one_if_max_sub_transformer {
     using sub_type   = T;          ///< The type on which the expression works
     using value_type = value_t<T>; ///< The type of valuie
 
     friend etl_traits<one_if_max_sub_transformer>;
 
-    static_assert(is_2d<sub_type>, "one_if_max_sub is only defined for 2D Matrix");
-
     static constexpr bool gpu_computable = impl::egblas::has_sone_if_max_sub && all_row_major<T> && all_floating<T>;
 
 private: