feat(example): currency and unmanned_aerial_vehicle examples added

example/currency.cpp

@@ -0,0 +1,84 @@
+// 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.
+
+#include <mp_units/iostream.h>
+#include <mp_units/quantity.h>
+#include <iostream>
+#include <map>
+
+using namespace mp_units;
+
+// clang-format off
+inline constexpr struct dim_currency : base_dimension<"$"> {} dim_currency;
+
+QUANTITY_SPEC(currency, dim_currency);
+
+inline constexpr struct euro : named_unit<"EUR", kind_of<currency>> {} euro;
+inline constexpr struct us_dollar : named_unit<"USD", kind_of<currency>> {} us_dollar;
+inline constexpr struct great_british_pound : named_unit<"GBP", kind_of<currency>> {} great_british_pound;
+inline constexpr struct japanese_jen : named_unit<"JPY", kind_of<currency>> {} japanese_jen;
+// clang-format on
+
+static_assert(!std::equality_comparable_with<quantity<euro, int>, quantity<us_dollar, int>>);
+
+#if 0
+
+// if you have only a few currencies to handle
+template<Unit auto From, Unit auto To>
+double exchange_rate()
+{
+  if constexpr (From == us_dollar && To == euro) return 0.9215;
+  else if constexpr (From == euro && To == us_dollar) return 1.0848;
+  // ...
+}
+
+#else
+
+std::string_view to_string_view(Unit auto u) { return u.symbol.ascii().c_str(); }
+
+template<Unit auto From, Unit auto To>
+double exchange_rate()
+{
+  static std::map<std::pair<std::string_view, std::string_view>, double> rates = {
+    {{"USD", "EUR"}, 0.9215}, {{"EUR", "USD"}, 1.0848},
+    // ...
+  };
+
+  return rates[std::make_pair(to_string_view(From), to_string_view(To))];
+}
+
+#endif
+
+template<ReferenceOf<currency> auto To>
+quantity<To, int> exchange_to(QuantityOf<currency> auto q)
+{
+  return static_cast<int>(exchange_rate<q.unit, get_unit(To)>() * q.number()) * euro;
+}
+
+int main()
+{
+  auto price_usd = 100 * us_dollar;
+  auto price_euro = exchange_to<euro>(price_usd);
+
+  std::cout << price_usd << " -> " << price_euro << "\n";
+  // std::cout << price_usd + price_euro << "\n";  // does not compile
+}