If …​ ElseIf chain has no Else clause

ID

vbnet.maintainability.else_if_needs_else

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Control Flow

Language

VB.NET

Description

Reports an If …​ ElseIf chain that ends without an Else clause. A chain of conditions with no final Else leaves the case where none of the conditions holds completely unhandled. A plain If …​ Then with no ElseIf is not reported - a single guarded action legitimately does nothing when its condition is false.

Rationale

Once a chain enumerates alternatives, the reader has to decide whether the missing Else is deliberate or an oversight, and nothing in the code answers that. At run time the unhandled case is silent: the variable being assigned keeps whatever value it already had, or the function falls through and returns the type default, and the caller cannot tell that from a real result. This is the classic failure when a new enum member, region code or status is introduced later and this chain is not updated.

The following code illustrates the pattern detected by this rule:

Public Function SurchargeFor(ByVal region As String) As Decimal
    Dim surcharge As Decimal = 0D
    ' FLAGGED: If ... ElseIf chain has no Else clause
    If region = "EU" Then
        surcharge = 4.5D
    ElseIf region = "US" Then
        surcharge = 6.25D
    End If
    Return surcharge
End Function

Remediation

Add a final Else that handles the remaining values explicitly - assign a documented default, log, or throw (for example ArgumentOutOfRangeException) so an unforeseen value fails loudly instead of being ignored. If the chain tests a single value against many alternatives, a Select Case with a Case Else expresses the same intent more clearly.

' Before: an unknown region silently yields 0
Dim surcharge As Decimal = 0D
If region = "EU" Then
    surcharge = 4.5D
ElseIf region = "US" Then
    surcharge = 6.25D
End If

' After: the unhandled case is explicit
Dim surcharge As Decimal
If region = "EU" Then
    surcharge = 4.5D
ElseIf region = "US" Then
    surcharge = 6.25D
Else
    Throw New ArgumentOutOfRangeException(NameOf(region))
End If

Configuration

This detector does not need any configuration.

References