Avoiding naming conflicts
A naming conflict occurs when you try to create or use an identifier that was previously defined. In some cases, naming conflicts generate errors such as Ambiguous name detected or Duplicate declaration in current scope. Naming conflicts that go undetected can result in bugs in your code that produce erroneous results, especially if you do not explicitly declare all variables before first use.
A naming conflict can occur when an identifier:
- Is visible at more than one scoping level.
- Has two different meanings at the same level.
For example, procedures in separate modules can have the same name. Therefore, you can define a procedure named
MySub in modules named
Mod2. No conflicts occur if each procedure is called only from other procedures in its own module. However, an error can occur if
MySub is called from a third module, and no qualification is provided to distinguish between the two
Most naming conflicts can be resolved by preceding each identifier with a qualifier that consists of the module name and, if necessary, a project name. For example:
The preceding code calls the Sub procedure
YourSub and passes
MyVar as an argument. You can use any combination of qualifiers to differentiate identical identifiers.
Visual Basic matches each reference to an identifier with the "closest" declaration of a matching identifier. For example, if
MyID is declared Public in two modules in a project (
Mod2), you can specify the
MyID declared in
Mod2 without qualification from within
Mod2, but you must qualify it as
Mod2.MyID to specify it in
This is also true if
Mod2 is in a different but directly referenced project. However, if
Mod2 is in an indirectly referenced project, that is, a project referenced by the project you directly reference, references to the
Mod2 variable named
MyID must always be qualified with the project name. If you reference
MyID from a third, directly referenced module, the match is made with the first declaration encountered by searching:
- Directly referenced projects, in the order that they appear in the References dialog box of the Tools menu.
- The modules of each project. Note that there is no inherent order to the modules in the project.
You can't reuse names of host-application objects, for example, R1C1 in Microsoft Excel, at different scoping levels.
Typical errors caused by naming conflicts include ambiguous names, duplicate declarations, undeclared identifiers, and procedures that are not found. By beginning each module with an Option Explicit statement to force explicit declarations of variables before they are used, you can avoid some potential naming conflicts and identifier-related bugs.
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