Changed the generation of method bodies to avoid duplication of local variables when a fixed instance is required.

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

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -1999,7 +1999,7 @@ namespace CppSharp.Generators.CSharp
             if (needsInstance)
             {
                 names.Insert(0, needsFixedThis ? string.Format("new global::System.IntPtr(&{0})",
-                    GeneratedIdentifier("instance")) : Helpers.InstanceIdentifier);
+                    GeneratedIdentifier("fixedInstance")) : Helpers.InstanceIdentifier);
             }
 
             if (needsFixedThis)
@@ -2007,7 +2007,7 @@ namespace CppSharp.Generators.CSharp
                 //WriteLine("fixed({0}* {1} = &this)", @class.QualifiedName,
                 //    GeneratedIdentifier("instance"));
                 //WriteStartBraceIndent();
-                WriteLine("var {0} = ToInternal();", Generator.GeneratedIdentifier("instance"));
+                WriteLine("var {0} = ToInternal();", Generator.GeneratedIdentifier("fixedInstance"));
             }
 
             if (needsReturn && !originalFunction.HasIndirectReturnTypeParameter)
@@ -2035,7 +2035,7 @@ namespace CppSharp.Generators.CSharp
             if (needsFixedThis)
             {
                 //    WriteCloseBraceIndent();
-                WriteLine("FromInternal(&{0});", Generator.GeneratedIdentifier("instance"));
+                WriteLine("FromInternal(&{0});", Generator.GeneratedIdentifier("fixedInstance"));
             }
 
             if (needsReturn)

tests/Basic/Basic.Tests.cs

@@ -129,6 +129,16 @@ public class BasicTests
         Assert.That(basic.test(new basic()), Is.EqualTo(5));
     }
 
+    [Test]
+    public void TestMethodWithFixedInstance()
+    {
+        var bar = new Bar2 { A = 1, B = 2, C = 3 };
+        Foo2 foo = bar.needFixedInstance();
+        Assert.AreEqual(foo.A, 1);
+        Assert.AreEqual(foo.B, 2);
+        Assert.AreEqual(foo.C, 3);
+    }
+
     [Test, Ignore]
     public void TestConversionOperator()
     {

tests/Basic/Basic.cpp

@@ -52,6 +52,16 @@ Bar2::operator Foo2()
     return f;
 }
 
+Foo2 Bar2::needFixedInstance() const
+{
+    Foo2 f;
+    f.A = A;
+    f.B = B;
+    f.C = C;
+
+    return f;
+}
+
 Hello::Hello ()
 {
     //cout << "Ctor!" << "\n";

tests/Basic/Basic.h

@@ -56,6 +56,7 @@ struct DLL_API Bar2 : public Bar
 
     operator int() const;
     operator Foo2();
+    Foo2 needFixedInstance() const;
 
     typedef void *Bar2::*FunctionPointerResolvedAsVoidStar;
     operator FunctionPointerResolvedAsVoidStar() const { return 0; }