Merge pull request #150 from dlang-community/fix_ref_returns

Fix #148
merged-on-behalf-of: Brian Schott <Hackerpilot@users.noreply.github.com>

Author: dlang-bot

src/containers/cyclicbuffer.d

@@ -226,23 +226,23 @@ struct CyclicBuffer(T, Allocator = Mallocator, bool supportGC = shouldAddGCRange
 	auto ref front(this This)() nothrow pure @property @safe
 	{
 		version (assert) if (empty) onRangeError();
-		alias ET = ContainerElementType!(This, T);
+		alias ET = ContainerElementType!(This, T, true);
 		return cast(ET) storage[start];
 	}
 
 	/// Accesses to the item at the end of the buffer.
 	auto ref back(this This)() nothrow pure @property @safe
 	{
 		version (assert) if (empty) onRangeError();
-		alias ET = ContainerElementType!(This, T);
+		alias ET = ContainerElementType!(This, T, true);
 		return cast(ET) storage[end];
 	}
 
 	/// buffer[i]
 	auto ref opIndex(this This)(size_t i) nothrow pure @safe
 	{
 		version (assert) if (i >= length) onRangeError();
-		alias ET = ContainerElementType!(This, T);
+		alias ET = ContainerElementType!(This, T, true);
 		return cast(ET) storage[(start + i) % $];
 	}
 

src/containers/hashmap.d

@@ -116,7 +116,7 @@ struct HashMap(K, V, Allocator = Mallocator, alias hashFunction = generateHash!K
 		import std.conv : text;
 		import std.exception : enforce;
 
-		alias CET = ContainerElementType!(This, V);
+		alias CET = ContainerElementType!(This, V, true);
 		size_t i;
 		auto n = find(key, i);
 		enforce(n !is null, "'" ~ text(key) ~ "' not found in HashMap");

src/containers/internal/element_type.d

@@ -7,7 +7,17 @@
 
 module containers.internal.element_type;
 
-template ContainerElementType(ContainerType, ElementType)
+/**
+ * Figures out the types that should be shown to users of the containers when
+ * functions such as front and opIndex are called.
+ *
+ * Params:
+ *     ContainerType = The container type, usually taken from a `this This`
+ *         template argument
+ *     ElementType = The type of the elements of the container.
+ *     isRef = If the type is being determined for a function that returns `ref`
+ */
+template ContainerElementType(ContainerType, ElementType, bool isRef = false)
 {
 	import std.traits : isMutable, hasIndirections, PointerTarget, isPointer, Unqual;
 
@@ -52,10 +62,12 @@ template ContainerElementType(ContainerType, ElementType)
 	}
 
 	static if (isMutable!ContainerType)
+	{
 		alias ContainerElementType = ElementType;
+	}
 	else
 	{
-		static if (hasIndirections!ElementType)
+		static if (isRef || hasIndirections!ElementType)
 			alias ContainerElementType = ET!(is(ContainerType == const), ElementType);
 		else
 			alias ContainerElementType = ElementType;

test/compile_test.d

@@ -340,8 +340,13 @@ private void checkSliceFunctionality(Type, Container)(ref Container container)
 
 private void checkIndexFunctionality(Type, KeyType, Container)(ref Container container)
 {
+	import std.traits : hasFunctionAttributes;
+
 	static assert(__traits(compiles, {container[KeyType.init];}));
-	static assert(is(typeof(container[KeyType.init]) == Type));
+	// The tests here will expect the wrong thing for opIndex implementations
+	// that return by ref.
+	static if (!hasFunctionAttributes!(Container.opIndex!Container, "ref"))
+		static assert(is(typeof(container[KeyType.init]) == Type));
 	static assert(is(typeof(container.length) == size_t));
 	assert(container.length == 0);
 }