added untag to simplify tag_cast'ing to no_tag

Author: gitsbi

quantity.hpp

@@ -729,6 +729,10 @@ template<typename U, typename S, typename V, typename T>
 constexpr auto tag_cast(const quantity<U,S,V,T>& q)                       {return implicit_quantity_caster<U,S,V,T,false,false,true>{q};}
 template<typename NewTag, typename U, typename S, typename V, typename T>
 constexpr auto tag_cast(const quantity<U,S,V,T>& q)                       {return quantity<U,S,V,NewTag>{tag_cast(q)};}
+template<typename U, typename V>
+constexpr auto untag(const quantity<U,V>& q)                              {return tag_cast<typename quantity<U,V>::untag::tag_type>(q);}
+template<typename U, typename V>
+constexpr auto untag(const quantity<U,V>& q)                              {return tag_cast<typename quantity<U,V>::untag::tag_type>(q);}
 /** @} */
 
 

test/test_quantity.cpp

@@ -584,7 +584,6 @@ SUBCASE("quantity casts") {
 	}
 
 	SUBCASE("testing tag_cast") {
-		using namespace unlib;
 		using test_qa  = test_quantity::retag<tag_t<struct tag_a>>;
 		using test_qb  = test_quantity::retag<tag_t<struct tag_b>>;
 
@@ -603,6 +602,12 @@ SUBCASE("quantity casts") {
 		CHECK(qa.get() == doctest::Approx(qb3.get()));
 	}
 
+	SUBCASE("testing untag") {
+		quantity_type qa{};
+
+		CHECK(typeid(untag(qa)) == typeid(quantity_type));
+	}
+
 	SUBCASE("testing quantity_cast") {
 		using test_qdka  = quantity<default_test_unit,  kilo_scaling, double, tag_t<struct tag_a>>;
 		using test_qika  = quantity<default_test_unit,  kilo_scaling, int   , tag_t<struct tag_a>>;