Extract NAPI VarPrefix and ArgumentPrefix to base class.

src/Generator/Generators/Marshal.cs

@@ -12,7 +12,7 @@ namespace CppSharp.Generators
             Cleanup = new TextGenerator { CurrentIndentation = indentation };
             VarPrefix = new TextGenerator();
             ArgumentPrefix = new TextGenerator();
-            this.Indentation = indentation;
+            Indentation = indentation;
         }
 
         public BindingContext Context { get; }
@@ -22,8 +22,8 @@ namespace CppSharp.Generators
         public TextGenerator Before { get; }
         public TextGenerator Return { get; }
         public TextGenerator Cleanup { get; }
-        public TextGenerator VarPrefix;
-        public TextGenerator ArgumentPrefix;
+        public TextGenerator VarPrefix { get; }
+        public TextGenerator ArgumentPrefix { get; }
 
         public string ReturnVarName { get; set; }
         public QualifiedType ReturnType { get; set; }

src/Generator/Generators/NAPI/NAPIMarshal.cs

@@ -337,15 +337,9 @@ namespace CppSharp.Generators.NAPI
 
     public class NAPIMarshalManagedToNativePrinter : MarshalPrinter<MarshalContext>
     {
-        public readonly TextGenerator VarPrefix;
-        public readonly TextGenerator ArgumentPrefix;
-
         public NAPIMarshalManagedToNativePrinter(MarshalContext ctx) 
             : base(ctx)
         {
-            VarPrefix = new TextGenerator();
-            ArgumentPrefix = new TextGenerator();
-
             Context.MarshalToNative = this;
         }
 
@@ -421,7 +415,7 @@ namespace CppSharp.Generators.NAPI
                 var isRef = Context.Parameter.Usage == ParameterUsage.Out ||
                     Context.Parameter.Usage == ParameterUsage.InOut;
 
-                ArgumentPrefix.Write("&");
+                Context.ArgumentPrefix.Write("&");
                 Context.Return.Write($"(::{@enum.QualifiedOriginalName}){0}{Context.Parameter.Name}",
                     isRef ? string.Empty : "*");
                 return true;
@@ -707,7 +701,7 @@ namespace CppSharp.Generators.NAPI
             var deref = isPointer ? "" : "*";
 
             if (!isPointer && Context.Parameter.Type.IsReference())
-                VarPrefix.Write("&");
+                Context.VarPrefix.Write("&");
 
             Context.Return.Write($"{deref}{instance}");
         }

src/Generator/Generators/NAPI/NAPISources.cs

@@ -861,9 +861,9 @@ namespace CppSharp.Generators.Cpp
                     NeedNewLine();
                 }
 
-                WriteLine($"auto {marshal.VarPrefix}{argName} = {marshal.Context.Return};");
-                paramMarshal.Prefix = marshal.ArgumentPrefix;
                 NewLineIfNeeded();
+                WriteLine($"auto {marshal.Context.VarPrefix}{argName} = {marshal.Context.Return};");
+                paramMarshal.Prefix = marshal.Context.ArgumentPrefix;
             }
 
             paramMarshal.Name = argName;