There are several compilations options available for Visual Basic source code and Option Strict defines compiler behavior for implicit
data type conversions. Specifying Option Strict Off will allow:
- Implicit narrowing conversions
- Late binding
- Implicit typing that results in an
Object type
This behavior can lead to unexpected runtime errors due to type mismatch or missing members.
Option Strict can be set in project properties or overridden in individual source files.
Noncompliant code example
Option Strict Off ' Noncompliant
Public Class KnownType
Public ReadOnly Property Name As String
End Class
Public Module MainMod
Public Function DoSomething(Arg) As String ' Type for "Arg" argument is not defined.
Dim Item As KnownType = Arg ' Implicit narrowing conversion doesn't enforce "Arg" to be of type "KnownType"
Return Arg.Title ' "Title" might not exist in "Arg"
End Function
End Module
Compliant solution
Option Strict On
Public Class KnownType
Public ReadOnly Property Name As String
End Class
Public Module MainMod
Public Function DoSomething(Arg As KnownType) As String
Dim Item As KnownType = Arg
Return Arg.Name
End Function
End Module
