Support default values of different type to target values in options

Support direct assignment of values to targets without lexical casts

1 files changed, 34 insertions, 4 deletions

diff --git a/project2/common/options.h b/project2/common/options.h
index b4cbaf8..2ccb7ec 100644
--- a/project2/common/options.h
+++ b/project2/common/options.h
@@ -7,6 +7,27 @@
 #include <list>
 #include <boost/lexical_cast.hpp>
 
+namespace std {
+	//
+	// Should be part of the standard headers, but seems to be missing
+	//
+	template<typename _Tp, typename _Up>
+		class __is_assignable_helper : public __sfinae_types {
+			template<typename _Tp1, typename _Up1>
+				static decltype(declval<_Tp1>() = declval<_Up1>(), __one()) __test(int);
+
+			template<typename, typename>
+				static __two __test(...);
+
+			public:
+			static constexpr bool value = sizeof(__test<_Tp, _Up>(0)) == 1;
+		};
+	/// is_assignable
+	template<typename _Tp, typename _Up>
+		struct is_assignable : public integral_constant<bool, __is_assignable_helper<_Tp, _Up>::value>
+	{ };
+}
+
 class Options {
 	public:
 		class Target;
@@ -43,10 +64,19 @@ class Options {
 					*target = T();
 				}
 				void assign(const Glib::ustring & value) const {
-					*target = boost::lexical_cast<T>(value);
+					doAssign(value);
 				}
 			protected:
 				T * target;
+			private:
+				template <typename dummy = int>
+				void doAssign(const Glib::ustring & value, typename boost::disable_if<std::is_assignable<T, Glib::ustring>, dummy>::type = 0) const {
+					*target = boost::lexical_cast<T>(value);
+				}
+				template <typename dummy = int>
+				void doAssign(const Glib::ustring & value, typename boost::enable_if<std::is_assignable<T, Glib::ustring>, dummy>::type = 0) const {
+					*target = value;
+				}
 		};
 
 		template <typename T> class TypedTarget<std::vector<T> > : public InstanceTarget {
@@ -66,9 +96,9 @@ class Options {
 				VofT * target;
 		};
 
-		template <typename T> class DefaultTypedTarget : public TypedTarget<T> {
+		template <typename T, typename D> class DefaultTypedTarget : public TypedTarget<T> {
 			public:
-				DefaultTypedTarget(T * t, const T & d) :
+				DefaultTypedTarget(T * t, const D & d) :
 					TypedTarget<T>(t),
 					defValue(d) {
 				}
@@ -104,7 +134,7 @@ class Options {
 		template <typename T, typename D>
 		static
 		TargetPtr value(T * t, const D & d) {
-			return new DefaultTypedTarget<T>(t, d);
+			return new DefaultTypedTarget<T, D>(t, d);
 		}
 
 		void reset() const;