Add metaprogramming constructors for vec1

- Tests, too

glm/detail/type_vec1.hpp

@@ -134,6 +134,12 @@ namespace glm
 		template <typename U, precision Q>
 		GLM_FUNC_DECL GLM_EXPLICIT tvec1(tvec1<U, Q> const & v);
 
+		/// Extra helper constructors for metaprogramming
+#		ifdef GLM_META_PROG_HELPERS
+		template <typename X, typename Y, typename Z = Y, typename W = Z>
+		GLM_FUNC_DECL tvec1(X const& x, Y const&, Z const& = Z(0), W const& = W(0));
+#		endif
+
 		// -- Swizzle constructors --
 
 #		if(GLM_HAS_ANONYMOUS_UNION && defined(GLM_SWIZZLE))

glm/detail/type_vec1.inl

@@ -93,6 +93,15 @@ namespace glm
 		: x(static_cast<T>(v.x))
 	{}
 
+	// -- Metaprogramming helper constructors --
+#	ifdef GLM_META_PROG_HELPERS
+	template <typename T, precision P>
+	template <typename X, typename Y, typename Z, typename W>
+	GLM_FUNC_QUALIFIER tvec1<T, P>::tvec1(X const& x, Y const&, Z const&, W const&)
+		: x(static_cast<T>(x))
+	{}
+#	endif
+
 	// -- Component accesses --
 
 #	ifdef GLM_FORCE_SIZE_FUNC

test/core/core_type_vec1.cpp

@@ -80,6 +80,17 @@ int test_vec1_ctor()
 		Error += std::is_copy_constructible<glm::vec1>::value ? 0 : 1;
 #	endif
 
+#	ifdef GLM_META_PROG_HELPERS
+	{
+		glm::vec1 a(1), b(1, 2), c(1, 2, 3), d(1, 2, 3, 4);
+
+		Error += (a == b) ? 0 : 1;
+		Error += (b == c) ? 0 : 1;
+		Error += (c == d) ? 0 : 1;
+		Error += (d == a) ? 0 : 1;
+	}
+#	endif
+
 /*
 #if GLM_HAS_INITIALIZER_LISTS
 	{