derived_dimension code split to a few smaller files

src/include/units/bits/derived_dimension_base.h

@@ -0,0 +1,61 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <units/base_dimension.h>
+#include <units/bits/external/downcasting.h>
+#include <units/exp.h>
+
+namespace units::detail {
+
+/**
+ * @brief A dimension of a derived quantity
+ *
+ * Expression of the dependence of a quantity on the base quantities (and their base dimensions) of a system of
+ * quantities as a product of powers of factors corresponding to the base quantities, omitting any numerical factors.
+ * A power of a factor is the factor raised to an exponent.
+ * 
+ * A derived dimension can be formed from multiple exponents (i.e. velocity is represented as "exp<L, 1>, exp<T, -1>").
+ * It is also possible to form a derived dimension with only one exponent (i.e. frequency is represented as just
+ * "exp<T, -1>").
+ * 
+ * @note This class template is used by the library engine and should not be directly instantiated by the user.
+ * 
+ * @tparam E a first exponent of a derived dimension
+ * @tparam ERest zero or more following exponents of a derived dimension
+ */
+template<Exponent E, Exponent... ERest>
+  requires (BaseDimension<typename E::dimension> && ... && BaseDimension<typename ERest::dimension>)
+struct derived_dimension_base : downcast_base<derived_dimension_base<E, ERest...>> {
+  using exponents = exp_list<E, ERest...>;
+};
+
+template<typename T>
+struct to_derived_dimension_base;
+
+template<Exponent... Es>
+struct to_derived_dimension_base<exp_list<Es...>> {
+  using type = derived_dimension_base<Es...>;
+};
+
+}  // namespace units::detail