Defer in Visual Basic .NET

Visual Basic .NET doesn’t have a direct equivalent to Go’s defer keyword. However, we can achieve similar functionality using the Try-Finally block. Here’s how we can implement the same concept:

Imports System
Imports System.IO

Module DeferExample
    Sub Main()
        ' Suppose we wanted to create a file, write to it,
        ' and then close when we're done. Here's how we could
        ' do that with Try-Finally.

        Dim f As StreamWriter = Nothing
        Try
            f = CreateFile("/tmp/defer.txt")
            WriteFile(f)
        Finally
            If f IsNot Nothing Then
                CloseFile(f)
            End If
        End Try
    End Sub

    Function CreateFile(ByVal p As String) As StreamWriter
        Console.WriteLine("creating")
        Try
            Return New StreamWriter(p)
        Catch ex As Exception
            Console.WriteLine($"Error: {ex.Message}")
            Environment.Exit(1)
            Return Nothing ' This line is never reached, but required by VB.NET
        End Try
    End Function

    Sub WriteFile(ByVal f As StreamWriter)
        Console.WriteLine("writing")
        f.WriteLine("data")
    End Sub

    ' It's important to check for errors when closing a
    ' file, even in a Finally block.
    Sub CloseFile(ByVal f As StreamWriter)
        Console.WriteLine("closing")
        Try
            f.Close()
        Catch ex As Exception
            Console.Error.WriteLine($"Error: {ex.Message}")
            Environment.Exit(1)
        End Try
    End Sub
End Module

In this Visual Basic .NET version:

We use a Try-Finally block to ensure that the file is closed after we’re done writing to it, regardless of whether an exception occurs or not.
The CreateFile function now returns a StreamWriter instead of a File object, as VB.NET typically uses StreamWriter for file writing operations.
Error handling is done using Try-Catch blocks instead of checking for nil errors.
We use string interpolation ($ strings) for formatting error messages.
The WriteFile function now takes a StreamWriter as an argument.
In the CloseFile function, we use Console.Error.WriteLine to print error messages to the standard error stream.

Running the program would produce output similar to the original:

creating
writing
closing

This example demonstrates how to use Try-Finally blocks in Visual Basic .NET to ensure proper resource cleanup, which is analogous to using defer in other languages.

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Defer in Visual Basic .NET