Merge pull request #3 from contour-terminal/improvement/cast_rval

Add rvalue operator. Update of test and documentation.

Author: christianparpart

README.md

@@ -11,6 +11,7 @@ This header can be simply copied into a project or used via CMake builtin functi
 
 # Simple usage
 
+Example of creation boxed structures and usage
 ``` c++
 
 #include <boxed-cpp/boxed.hpp>
@@ -39,6 +40,28 @@ int main()
 
 ```
 
+
+When you need to get value from boxed type, you need to unbox it
+``` c++
+//unbox in declared type. double in this case
+auto speed_value_native = unbox(speed_of_light);
+//unbox into float type
+auto speed_value_float = unbox<float>(speed_of_light);
+// unbox into int type
+auto speed_value_int = unbox<int>(speed_of_light);
+```
+
+
+You can also evaluate expressions with boxed types without the need of unboxing them if explicitly declare the resulted type
+``` c++
+auto speed_of_light = Speed(299792458.0);
+auto value = speed_of_light * 2.0; // type of value is Speed
+
+// boxed value will be automatically unboxed into type that was boxed, in this case double
+double value_d = speed_of_light * 2.0;
+```
+
+
 # More advanced usage
 You can forget about the order of parameters in your code
 

include/boxed-cpp/boxed.hpp

@@ -68,6 +68,7 @@ struct boxed
 
     [[nodiscard]] constexpr T& get() noexcept { return value; }
     [[nodiscard]] constexpr T const& get() const noexcept { return value; }
+    constexpr operator T() const && {return value;}
 
     template <typename To>
     [[nodiscard]] constexpr auto as() const noexcept

test-boxed-cpp.cpp

@@ -15,6 +15,7 @@
 #include <boxed-cpp/boxed.hpp>
 #include <catch2/catch.hpp>
 #include <limits>
+#include <type_traits>
 
 namespace tags { struct Length{}; struct From{}; struct To{}; }
 
@@ -80,3 +81,32 @@ TEST_CASE("function with boxed variables")
     auto value = std::abs(unbox( wave_speed(vacuum_permittivity, vacuum_permeability) - speed_of_light ));
     REQUIRE(value < std::numeric_limits<double>::epsilon());
 }
+
+TEST_CASE("unbox types check")
+{
+    auto speed_of_light = Speed(299792458.0);
+    auto speed_value_native = unbox(speed_of_light);
+    static_assert(std::is_same_v<decltype(speed_value_native),double>);
+    auto speed_value_float = unbox<float>(speed_of_light);
+    static_assert(std::is_same_v<decltype(speed_value_float),float>);
+    auto speed_value_int = unbox<int>(speed_of_light);
+    static_assert(std::is_same_v<decltype(speed_value_int),int>);
+}
+
+
+TEST_CASE("unbox without template parameters to initial type")
+{
+    auto speed_of_light = Speed(299792458.0);
+    REQUIRE( std::abs(unbox(speed_of_light) - 299792458.0) < std::numeric_limits<double>::epsilon());
+}
+
+TEST_CASE("cast inside rvalue")
+{
+    auto speed_of_light = Speed(299792458.0);
+
+    auto distance_auto = speed_of_light * 2.0;
+    static_assert(std::is_same_v<decltype(distance_auto),Speed>);
+
+    double distance_d = speed_of_light * 2.0;
+    REQUIRE(distance_d - 2.0 * 299792458.0 < std::numeric_limits<double>::epsilon());
+}