CStr() compared with .ToString when dealing with an Enum type

Question

I (obviously incorrectly) had assumed that Cstr(something) was equivalent to something.ToString.
I wanted to get hold of an enumerated type as a string and it seems depending on which conversion method I use I either get the index of the enum or the name:

Public Enum vehicleType
    Car
    Lorry
    Bicycle
End Enum

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        MsgBox("Index is " & _
               CStr(vehicleType.Car) & _
               ".Name is " & _
               vehicleType.Car.ToString)
    End Sub
End Class

Why are these conversions to string returning different elements of the enum type?

Answer 1

The ToString method is a standard public method that returns a String. It is a method that is defined by the base Object type as overrideable. Each class can, therefore, override that method to return anything that it wants. It is quite common for classes to override the ToString method to make it return a nice human-readable description of the object.

CStr, on the other hand, is a casting operator. It is shorthand for CType(x, String). The casting operator, like many other operators, can be overridden by any class. Normally, though, you want casting operations to return the closest representation of the actual value of the original object, rather than a descriptive string.

It is not unusual then, that you may want ToString to return a different result than CStr. In the case of an enum, each member is essentially an Integer, so CStr on an enum member works the same as CStr on an integer. That is what you would expect. However, ToString has been overridden to return the more human readable version of the value. That is also what you would expect.

Here's an example of a class that overrides both CStr and ToString:

Public Class MyClass
    Public Overrides Function ToString()
        Return "Result from ToString"
    End Function

    Public Shared Widening Operator CType(ByVal p1 As MyClass) As String
        Return "Result from cast to String"
    End Operator
End Class

Answer 2

What type of expressions CStr() accepts is explained in detail in this MSDN Library article. Summarizing:

• An expression that produces a Boolean, converted to "True" or "False"
• An expression that produces a DateTime, converted to the short datetime format
• An expression that produces a numeric type, converted to a string that represents the number.

Do note that it doesn't have a bullet for enumerated types. The compiler is always happy to convert an enum value to an integer. So the 3rd bullet applies and this is why you get "0".