Allow getting members by name from ClassBuilder.

src/tink/macro/ClassBuilder.hx

@@ -124,7 +124,11 @@ class ClassBuilder {
 		}
 		return superFields.get(name);
 	}
-	
+	public function memberByName(name:String, ?pos:Position)
+		return
+			if (memberMap.exists(name)) Success(memberMap.get(name));
+			else pos.makeFailure('unknown member $name');
+			
 	public function removeMember(member:Member):Bool 
 		return 
 			member != null 

src/tink/macro/Constructor.hx

@@ -92,9 +92,9 @@ class Constructor {
 		var tmp = MacroApi.tempName();
 		
 		if (options.bypass) {
-			switch @:privateAccess owner.memberMap[name] {
-				case nil if (nil == null):
-				case member: member.addMeta(':isVar');
+			switch owner.memberByName(name) {
+				case Success(member): member.addMeta(':isVar');
+				default:
 			}
 			
 			if (Context.defined('dce') && Context.definedValue('dce') == 'full') {