Custom Errors in Visual Basic .NET

Custom errors can be implemented in Visual Basic .NET by creating a custom exception class that inherits from the Exception class. Here’s an example that demonstrates this concept:

Imports System

' A custom error type usually has the suffix "Exception".
Public Class ArgException
    Inherits Exception

    Public Property Arg As Integer

    Public Sub New(arg As Integer, message As String)
        MyBase.New(message)
        Me.Arg = arg
    End Sub

    Public Overrides Function ToString() As String
        Return $"{Arg} - {Message}"
    End Function
End Class

Module Program
    Function F(arg As Integer) As Integer
        If arg = 42 Then
            ' Throw our custom exception.
            Throw New ArgException(arg, "can't work with it")
        End If
        Return arg + 3
    End Function

    Sub Main()
        Try
            Dim result = F(42)
        Catch ex As ArgException
            ' In VB.NET, we use TypeOf to check the exception type
            Console.WriteLine(ex.Arg)
            Console.WriteLine(ex.Message)
        Catch ex As Exception
            Console.WriteLine("err doesn't match ArgException")
        End Try
    End Sub
End Module

In this example, we define a custom exception class ArgException that inherits from the Exception class. This is similar to implementing the error interface in Go.

The F function demonstrates how to throw the custom exception when a specific condition is met.

In the Main subroutine, we use a Try-Catch block to handle exceptions. This is equivalent to error handling in Go. The TypeOf keyword is used to check if the caught exception is of type ArgException, which is similar to using errors.As in Go.

To run this program:

$ vbc CustomErrors.vb
$ CustomErrors.exe
42
can't work with it

In Visual Basic .NET, exception handling is used for error management, which is somewhat different from Go’s approach of returning errors. However, the concept of creating and using custom error types remains similar.

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Custom Errors in Visual Basic .NET