Remove the copying of returned values

This improves performance and more importantly, fixes a memory leak caused by the original value not being destroyed.

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -289,8 +289,13 @@ namespace CppSharp.Generators.CSharp
 
             if (returnType.IsAddress())
                 Context.Return.Write(HandleReturnedPointer(@class, qualifiedClass.Type));
-            else
-                Context.Return.Write($"{qualifiedClass}.{Helpers.CreateInstanceIdentifier}({Context.ReturnVarName})");
+            else if (Context.MarshalKind == MarshalKind.NativeField ||
+                Context.Function?.HasIndirectReturnTypeParameter == true ||
+                Context.Function?.OperatorKind == CXXOperatorKind.Subscript)
+                Context.Return.Write($@"{qualifiedClass}.{Helpers.CreateInstanceIdentifier}({
+                    Context.ReturnVarName})");
+            else Context.Return.Write($@"{qualifiedClass}.{Helpers.CreateInstanceIdentifier}(new {
+                    typePrinter.IntPtrType}(&{Context.ReturnVarName}))");
 
             return true;
         }

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -2808,6 +2808,7 @@ namespace CppSharp.Generators.CSharp
 
             var originalFunction = function.OriginalFunction ?? function;
 
+            var names = new List<string>();
             if (originalFunction.HasIndirectReturnTypeParameter)
             {
                 var indirectRetType = originalFunction.Parameters.First(
@@ -2825,8 +2826,8 @@ namespace CppSharp.Generators.CSharp
                     Class retClass;
                     type.TryGetClass(out retClass);
                     var @class = retClass.OriginalClass ?? retClass;
-                    WriteLine($@"var {Helpers.ReturnIdentifier} = new {
-                        TypePrinter.PrintNative(@class)}();");
+                    WriteLine($@"var {Helpers.ReturnIdentifier} = Marshal.AllocHGlobal({
+                        @class.Layout.GetSize()});");
                 }
                 else
                 {
@@ -2839,13 +2840,15 @@ namespace CppSharp.Generators.CSharp
 
                         WriteLine("{0} {1};", typeMap.CSharpSignatureType(typePrinterContext),
                             Helpers.ReturnIdentifier);
+                        names.Add($"new IntPtr(&{Helpers.ReturnIdentifier})");
                     }
                     else
                         WriteLine("var {0} = {1};", construct);
                 }
+                if (names.Count == 0)
+                    names.Add(Helpers.ReturnIdentifier);
             }
 
-            var names = new List<string>();
             foreach (var param in @params)
             {
                 if (param.Param == operatorParam && needsInstance)
@@ -2862,12 +2865,6 @@ namespace CppSharp.Generators.CSharp
 
             var needsFixedThis = needsInstance && isValueType;
 
-            if (originalFunction.HasIndirectReturnTypeParameter)
-            {
-                var name = string.Format("new IntPtr(&{0})", Helpers.ReturnIdentifier);
-                names.Insert(0, name);
-            }
-
             if (needsInstance)
             {
                 var instanceIndex = GetInstanceParamIndex(method);

src/Generator/Types/Std/Stdlib.cs

@@ -382,8 +382,7 @@ namespace CppSharp.Types.Std
                 ctx.MarshalKind == MarshalKind.ReturnVariableArray;
             ctx.Before.WriteLine($@"var {varBasicString} = {
                 basicString.Visit(typePrinter)}.{Helpers.CreateInstanceIdentifier}({
-                (usePointer ? string.Empty : $"new {typePrinter.IntPtrType}(&")}{
-                 ctx.ReturnVarName}{(usePointer ? string.Empty : ")")});");
+                 ctx.ReturnVarName});");
             string @string = $"{qualifiedBasicString}Extensions.{data.Name}({varBasicString})";
             if (usePointer)
             {