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ByRef object arguments taking with multiple types

VB6 is allows almost many implicit conversion of actual arguments to formal argument, but C# does not.  

Consider rvarItem the following example.  In the calling code, is used to return different types of variables from a weakly types collection:

Public Function g_Collection_ItemIsDefined(ByVal vobjCollection As Object, Optional ByVal vvarItem As Variant, Optional ByVal vstrKey As String, _
    Optional ByRef rvarItem As Variant) As Boolean

Furthermore, suppose g_Collection_ItemIsDefined is called with many different types of actual arguments passed to the rvarItem so the tool chooses to declare the formal argument as type object.  However, passing an argument by ref is in .NET requires strict typing and to build within this constraint, the tool must introduce a temporary variable to box the actual argument.  These are named argTemp1, argTetmp2... argTempN with numbering starting at 1 within each file.  For example, passing a boolean to a ref object looks like this:

object argTemp1 = blnOperationEnabled;
if (basCollection.g_Collection_ItemIsDefined(colItemOperations,null,strOperation,ref argTemp1))

By default the argTemp variable is ONLY initialized from the actual argument and used in the call. It is not moved back to the actual argument after the call. In some cases, ignoring the change to a ByRef argument is a breaking change from the VB6 that must be addressed using various techniques depending on the situation. One possible technique is to use the Refactor/Overload as described here.

Refactor/Overload is a translation script command (gmPL) command that may be be added to the Compile block in your translation script as in the following example:

...
<Compile Project="..." >
<Refactor>
<OverLoad Identifier="Project1.Form1.MySub.o_Var" Types="Boolean" />
</Refactor>
</Compile>
...
where
Identifier  is the fully qualified identifier of the argument to overload
Types       is a list of source types known to the tool.  This can include gmStudio's VB6 types, application types, and external COM types

The effect of adding a refactor/overload command is three-fold:

1) The tool will report warnings about other types used with the argument.  These warnings can be used to add more types ot the Types list. For example:

Warning#3005: Passing <App.frmClientGroupSelect.m_DisplayedClientGroupColumns_AdjustColumnHeaders.chdSortColumnHeader> with type <MSComctlLib.ColumnHeader> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.frmRecipeBookSelect.m_DisplayedRecipeBookColumns_AdjustColumnHeaders.chdSortColumnHeader> with type <MSComctlLib.ColumnHeader> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.frmFoodClassSelect.m_FoodClass_Populate.nodFoodClass> with type <MSComctlLib.Node> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.frmFoodClassSelect.m_FoodClass_PopulateChildren.nodParentFoodClass> with type <MSComctlLib.Node> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.frmClientSelect.m_Clients_Populate.lsiClient> with type <MSComctlLib.ListItem> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.frmClientSelect.m_DisplayedClientColumns_AdjustColumnHeaders.chdSortColumnHeader> with type <MSComctlLib.ColumnHeader> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
....
Warning#3005: Passing <App.g_VBObject_SetEnabled.colContainerContents> with type <Collection> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.g_VBObjects_LoadContainers.colContainerContents> with type <Collection> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.g_DragCursor_Set.colItemTypeItems> with type <Collection> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>
Warning#3005: Passing <App.g_RecentItems_Add.strRecentItem> with type <String> to <App.g_Collection_ItemIsDefined.rvarItem> with type <Variant>

2) The tool will generated an overload of the method for each type in Types.  These overloads deal with marshalling different variables to the weakly typed formal argument in the implementation.  Notice that in the wrapper, the temporary arg is moved back actual arg after the call. For example:

      public static bool g_Collection_ItemIsDefined(object vobjCollection,object vvarItem,string vstrKey,ref bool rvarItem)
      {
         object TemporaryArg1 = rvarItem;
         bool retVal = g_Collection_ItemIsDefined(vobjCollection,vvarItem,vstrKey,ref TemporaryArg1);
         rvarItem = Convert.ToBoolean(TemporaryArg1);
         return retVal;
      }

3) The tool  removes the use of the ref tempArg from the calls where an actual arg of one of the types in Types is passed.  For example, the using argTemp1 shown above becomes simply:

if (basCollection.g_Collection_ItemIsDefined(colItemOperations,null,strOperation,ref blnOperationEnabled))

 

Refactor Generic

<Compile Project="..." >
<Refactor>
<Generic identifier="Project1.Form1.MySub.o_Var" Types="Integer,String" />
</Refactor>
</Compile>
 

 

 

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