PRB: Naming Conflicts Between Variables and Objects

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

Conflicts between the names of various constructs produce errors in Visual Basic version 4.0.

CAUSE

Problems of this type are caused by not taking into account the scope of variables and objects. When a conflict occurs, Visual Basic gives precedence to constructs of a narrower scope over those of a broader scope. Some cases of this type can be handled by Visual Basic's design time syntax checker, but others must be handled later (called late binding) in order to permit more versatility.

RESOLUTION

Use unique names for variables, objects, and other constructs whenever possible. When this is not possible, such as with type libraries, specify a fully qualified name (for example, OpenDialog.Help_Button) to avoid potential conflicts.

STATUS

This behavior is by design.

MORE INFORMATION

Variables

Variables have three possible levels of scope: local, module, and global. If two variables of the same name are defined, Visual Basic uses the variable of the narrowest scope. Therefore, by using unique names for local variables, you can avoid a problem.

Type and Object Libraries

Multiple type libraries may use the same name but give different values. The ShowHelp flag of the Common Dialog control has different values for each type of dialog that uses it. Attempting to refer to just ShowHelp produces the diagnostic "Ambiguous name detected" at run time.

To avoid conflicts, specify the fully qualified name of the construct, such as FileOpenConstants.ShowHelp. The "Ambiguous name detected" topic in the Help file describes the following other ways this message can be produced:

• More than one object in the same scope may have elements with the same name. Qualify the element name by including the object name and a period. For example:

        Object.Property
  

• Module-level identifiers and project-level identifiers (module names and referenced project names) may be reused in a procedure although it makes programs harder to maintain and debug. However, if you want to refer to both items in the same procedure, the item having wider scope must be qualified. For example, if MyID is declared at the module level of MyModule, and then a procedure-level variable is declared with the same name in the module, references to the module-level variable must be appropriately qualified:

        Dim MyID As String
  

        Sub MySub
           MyModule.MyID = "This is module-level variable"
           Dim MyID As String
           MyID = "This is the procedure-level variable"
           Debug.Print MyID
           Debug.Print MyModule.MyID
        End Sub
  
  

• An identifier declared at module level conflicts with a procedure name. For example, this error occurs if the variable MyID is declared at module level, and then a procedure is defined with the same name:

        Public MyID
  

        Sub MyID
           '. . .
        End Sub
  
     In this case, change one of the names because modification with a common
     module name would not resolve the ambiguity. Note that procedure names
     are Public by default, but variable names are Private unless specified
     as Public.
  
  

Form and Module Names

Using the name of an internal function as the name of a Module, such as String.BAS, produces no diagnostic in the IDE. Attempting to run the program with references to the String$() functions produces the following diagnostic:

   Expected variable or procedures, not module

Keywords          : PrgOther VB4ALL VB4WIN vbwin GnrlVb kbprg
Technology        : kbvba
Version           : WINDOWS:4.0
Platform          : WINDOWS
Issue type        : kbprb