Fix inability to 'co_yield' a non-const T& from generator<const T>.

lewissbaker · lewissbaker · commit c6a25679f7a0 · 2019-01-01T21:16:06.000-08:00
Fixes lewissbaker#88.
diff --git a/include/cppcoro/generator.hpp b/include/cppcoro/generator.hpp
@@ -34,9 +34,9 @@ namespace cppcoro
 			constexpr std::experimental::suspend_always final_suspend() const { return {}; }
 
 			template<
-				typename U,
-				typename = std::enable_if_t<std::is_same<U, T>::value>>
-			std::experimental::suspend_always yield_value(U& value) noexcept
+				typename U = T,
+				std::enable_if_t<!std::is_lvalue_reference<U>::value, int> = 0>
+			std::experimental::suspend_always yield_value(T& value) noexcept
 			{
 				m_value = std::addressof(value);
 				return {};
diff --git a/test/generator_tests.cpp b/test/generator_tests.cpp
@@ -60,6 +60,31 @@ TEST_CASE("generator of reference returns by reference")
 	CHECK(value == 2.0f);
 }
 
+TEST_CASE("generator of const type")
+{
+	auto fib = []() -> generator<const std::uint64_t>
+	{
+		std::uint64_t a = 0, b = 1;
+		while (true)
+		{
+			co_yield b;
+			b += std::exchange(a, b);
+		}
+	};
+
+	std::uint64_t count = 0;
+	for (auto i : fib())
+	{
+		if (i > 1'000'000) {
+			break;
+		}
+		++count;
+	}
+
+	// 30th fib number is 832'040
+	CHECK(count == 30);
+}
+
 TEST_CASE("generator doesn't start until its called")
 {
 	bool reachedA = false;
