Warns about parameters passed by value being assigned a new value in the body of a procedure.

Inspection type: CodeQualityIssues

Default severity: Warning


Debugging is easier if the procedure's initial state is preserved and accessible anywhere within its scope. Mutating the inputs destroys the initial state, and makes the intent ambiguous: if the calling code is meant to be able to access the modified values, then the parameter should be passed ByRef; the ByVal modifier might be a bug


The following quick-fixes are available for this inspection:

  • IgnoreOnce: Adds an '@Ignore annotation to ignore a specific inspection result. Applicable to all inspections whose results can be annotated in a module.
  • AssignedByValParameterMakeLocalCopy: Introduces a new local variable and assigns it at the top of the procedure scope, then updates all parameter references to refer to the new local variable.
  • IgnoreInModule: Adds an '@IgnoreModule annotation to ignore a inspection results for a specific inspection inside a whole module. Applicable to all inspections whose results can be annotated in a module.
  • PassParameterByReference: Modifies a parameter to be passed by reference.


Each example is a self-contained MCVE showing the feature in a single specific scenario.

Standard Module
Named Module1 by default, these are general-purpose standard procedural modules.
Class Module
Named Class1 by default, these modules define the default interface for an object of that type.
Predeclared Class
A class module with its VB_PredeclaredId attribute set to True (with or without a @PredeclaredId annotation).
Interface Module
Abstract interfaces are class modules (with or without an @Interface annotation) whose default interface is not a class type intended to be instantiated.
UserForm Module
A predeclared class with a design-time visual designer using the MSForms UI framework.
Document Module
Owned by the host application, these class modules belong to the host document and may handle various events fired by the host application.

The following code should trigger this inspection:


Public Sub DoSomething(ByVal foo As Long)
    foo = foo + 1 ' is the caller supposed to see the updated value?
    Debug.Print foo
End Sub

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