Merge pull request #92 from pbackus/access-by-index

Refactor: access SumType value by index, not type

Author: pbackus

src/sumtype.d

@@ -256,6 +256,8 @@ private enum hasPostblit(T) = __traits(hasPostblit, T);
 
 private enum isInout(T) = is(T == inout);
 
+private enum memberName(size_t tid) = "values_" ~ toCtString!tid;
+
 // Workaround for dlang issue 19669
 private enum haveDip1000 = __traits(compiles, () @safe {
 	int x;
@@ -300,45 +302,41 @@ private:
 
 	union Storage
 	{
-		// Workaround for dlang issue 20068
-		template memberName(T)
-			if (IndexOf!(T, Types) >= 0)
-		{
-			enum tid = IndexOf!(T, Types);
-			mixin("enum memberName = `values_", toCtString!tid, "`;");
-		}
-
-		static foreach (T; Types) {
-			mixin("T ", memberName!T, ";");
+		static foreach (tid, T; Types) {
+			/+
+			Giving these fields individual names makes it possible to use brace
+			initialization for Storage.
+			+/
+			mixin("T ", memberName!tid, ";");
 		}
 	}
 
 	Storage storage;
 	Tag tag;
 
 	/**
-	 * Accesses the value stored in a SumType.
+	 * Accesses the value stored in a SumType by its index.
 	 *
 	 * This method is memory-safe, provided that:
 	 *
 	 *   1. A SumType's tag is always accurate.
-	 *   2. A SumType cannot be assigned to in @safe code if that assignment
-	 *      could cause unsafe aliasing.
+	 *   2. A SumType's value cannot be unsafely aliased in @safe code.
 	 *
 	 * All code that accesses a SumType's tag or storage directly, including
 	 * @safe code in this module, must be manually checked to ensure that it
 	 * does not violate either of the above requirements.
 	 */
 	@trusted
-	ref inout(T) get(T)() inout
-		if (IndexOf!(T, Types) >= 0)
+	// Explicit return type omitted
+	// Workaround for https://github.com/dlang/dmd/issues/20549
+	ref get(size_t tid)() inout
+		if (tid < Types.length)
 	{
-		enum tid = IndexOf!(T, Types);
 		assert(tag == tid,
-			"This `" ~ SumType.stringof ~
-			"` does not contain a(n) `" ~ T.stringof ~ "`"
+			"This `" ~ SumType.stringof ~ "`" ~
+			"does not contain a(n) `" ~ Types[tid].stringof ~ "`"
 		);
-		return __traits(getMember, storage, Storage.memberName!T);
+		return storage.tupleof[tid];
 	}
 
 public:
@@ -351,9 +349,9 @@ public:
 
 			static if (isCopyable!T) {
 				// Workaround for dlang issue 21542
-				__traits(getMember, storage, Storage.memberName!T) = __ctfe ? value : forward!value;
+				storage.tupleof[tid] = __ctfe ? value : forward!value;
 			} else {
-				__traits(getMember, storage, Storage.memberName!T) = forward!value;
+				storage.tupleof[tid] = forward!value;
 			}
 
 			tag = tid;
@@ -365,7 +363,7 @@ public:
 				/// ditto
 				this(const(T) value) const
 				{
-					__traits(getMember, storage, Storage.memberName!T) = value;
+					storage.tupleof[tid] = value;
 					tag = tid;
 				}
 			}
@@ -378,7 +376,7 @@ public:
 				/// ditto
 				this(immutable(T) value) immutable
 				{
-					__traits(getMember, storage, Storage.memberName!T) = value;
+					storage.tupleof[tid] = value;
 					tag = tid;
 				}
 			}
@@ -392,7 +390,7 @@ public:
 				this(Value)(Value value) inout
 					if (is(Value == DeducedParameterType!(inout(T))))
 				{
-					__traits(getMember, storage, Storage.memberName!T) = value;
+					storage.tupleof[tid] = value;
 					tag = tid;
 				}
 			}
@@ -414,10 +412,9 @@ public:
 				storage = other.match!((ref value) {
 					alias OtherTypes = Map!(InoutOf, Types);
 					enum tid = IndexOf!(typeof(value), OtherTypes);
-					alias T = Types[tid];
 
 					mixin("inout(Storage) newStorage = { ",
-						Storage.memberName!T, ": value",
+						memberName!tid, ": value",
 					" };");
 
 					return newStorage;
@@ -431,10 +428,10 @@ public:
 				this(ref SumType other)
 				{
 					storage = other.match!((ref value) {
-						alias T = typeof(value);
+						enum tid = IndexOf!(typeof(value), Types);
 
 						mixin("Storage newStorage = { ",
-							Storage.memberName!T, ": value",
+							memberName!tid, ": value",
 						" };");
 
 						return newStorage;
@@ -453,10 +450,9 @@ public:
 					storage = other.match!((ref value) {
 						alias OtherTypes = Map!(ConstOf, Types);
 						enum tid = IndexOf!(typeof(value), OtherTypes);
-						alias T = Types[tid];
 
 						mixin("const(Storage) newStorage = { ",
-							Storage.memberName!T, ": value",
+							memberName!tid, ": value",
 						" };");
 
 						return newStorage;
@@ -475,10 +471,9 @@ public:
 					storage = other.match!((ref value) {
 						alias OtherTypes = Map!(ImmutableOf, Types);
 						enum tid = IndexOf!(typeof(value), OtherTypes);
-						alias T = Types[tid];
 
 						mixin("immutable(Storage) newStorage = { ",
-							Storage.memberName!T, ": value",
+							memberName!tid, ": value",
 						" };");
 
 						return newStorage;
@@ -549,12 +544,13 @@ public:
 				this.match!destroyIfOwner;
 
 				static if (isCopyable!T) {
+					// Workaround for dlang issue 21542
 					mixin("Storage newStorage = { ",
-						Storage.memberName!T, ": __ctfe ? rhs : forward!rhs",
+						memberName!tid, ": __ctfe ? rhs : forward!rhs",
 					" };");
 				} else {
 					mixin("Storage newStorage = { ",
-						Storage.memberName!T, ": forward!rhs",
+						memberName!tid, ": forward!rhs",
 					" };");
 				}
 
@@ -1005,7 +1001,7 @@ version (D_BetterC) {} else
 	alias MySum = SumType!(ubyte, void*[2]);
 
 	MySum x = [null, cast(void*) 0x12345678];
-	void** p = &x.get!(void*[2])[1];
+	void** p = &x.get!1[1];
 	x = ubyte(123);
 
 	assert(*p != cast(void*) 0x12345678);
@@ -1034,8 +1030,8 @@ version (D_BetterC) {} else
 	} catch (Exception e) {}
 
 	assert(
-		(x.tag == 0 && x.get!A.value == 123) ||
-		(x.tag == 1 && x.get!B.value == 456)
+		(x.tag == 0 && x.get!0.value == 123) ||
+		(x.tag == 1 && x.get!1.value == 456)
 	);
 }
 
@@ -1093,8 +1089,8 @@ version (D_BetterC) {} else
 	SumType!(S[1]) x = [S(0)];
 	SumType!(S[1]) y = x;
 
-	auto xval = x.get!(S[1])[0].n;
-	auto yval = y.get!(S[1])[0].n;
+	auto xval = x.get!0[0].n;
+	auto yval = y.get!0[0].n;
 
 	assert(xval != yval);
 }
@@ -1169,8 +1165,8 @@ version (D_BetterC) {} else
 	SumType!S y;
 	y = x;
 
-	auto xval = x.get!S.n;
-	auto yval = y.get!S.n;
+	auto xval = x.get!0.n;
+	auto yval = y.get!0.n;
 
 	assert(xval != yval);
 }
@@ -1241,8 +1237,8 @@ version (D_BetterC) {} else
 	SumType!S x = S();
 	SumType!S y = x;
 
-	auto xval = x.get!S.n;
-	auto yval = y.get!S.n;
+	auto xval = x.get!0.n;
+	auto yval = y.get!0.n;
 
 	assert(xval != yval);
 }
@@ -1783,10 +1779,10 @@ private template matchImpl(Flag!"exhaustive" exhaustive, handlers...)
 			 * argument's tag, so there's no need to use TagTuple.
 			 */
 			enum handlerArgs(size_t caseId) =
-				"args[0].get!(SumTypes[0].Types[" ~ toCtString!caseId ~ "])()";
+				"args[0].get!(" ~ toCtString!caseId ~ ")()";
 
 			alias valueTypes(size_t caseId) =
-				typeof(args[0].get!(SumTypes[0].Types[caseId])());
+				typeof(args[0].get!(caseId)());
 
 			enum numCases = SumTypes[0].Types.length;
 		// Multiple dispatch (slow path)
@@ -1810,9 +1806,7 @@ private template matchImpl(Flag!"exhaustive" exhaustive, handlers...)
 
 				template getType(size_t i)
 				{
-					enum tid = tags[i];
-					alias T = SumTypes[i].Types[tid];
-					alias getType = typeof(args[i].get!T());
+					alias getType = typeof(args[i].get!(tags[i])());
 				}
 
 				alias valueTypes = Map!(getType, Iota!(tags.length));
@@ -2015,8 +2009,7 @@ template handlerArgs(size_t caseId, typeCounts...)
 	static foreach (i; 0 .. tags.length) {
 		handlerArgs = AliasSeq!(
 			handlerArgs,
-			"args[" ~ toCtString!i ~ "].get!(SumTypes[" ~ toCtString!i ~ "]" ~
-			".Types[" ~ toCtString!(tags[i]) ~ "])(), "
+			"args[" ~ toCtString!i ~ "].get!(" ~ toCtString!(tags[i]) ~ ")(), "
 		);
 	}
 }
@@ -2264,7 +2257,7 @@ version (D_Exceptions)
 		(ref double d) { d *= 2; }
 	);
 
-	assert(value.get!double.isClose(6.28));
+	assert(value.get!1.isClose(6.28));
 }
 
 // Handlers that return by ref