Migrating Legacy Visual Basic

Private Type BookRecord
    Title As String
    Copies As Integer          ' 16 bits
End Type

Private Sub AddCopy(copies As Long)    ' ByRef, because nothing was written
    copies = copies + 1
End Sub

Private Sub Demo()
    Dim anything As Variant
    Dim shelf1 As Book, shelf2 As Book
    anything = 42
    Set shelf1 = New Book
    Set shelf2 = shelf1
    shelf2.Title = "Emma"
End Sub

Option Strict On

Module M01TypesAndAssignment
    Public Structure BookRecord
        Public Title As String
        Public Copies As Short
        Public Price As Decimal
    End Structure

    Public Class Book
        Public Property Title As String = ""
    End Class

    Sub AddCopyByDefault(copies As Integer)
        copies += 1
    End Sub

    Sub AddCopyByRef(ByRef copies As Integer)
        copies += 1
    End Sub

    Sub Main()
        Console.WriteLine($"Short   is System.{GetType(Short).Name}, {Short.MinValue} to {Short.MaxValue}")
        Console.WriteLine($"Integer is System.{GetType(Integer).Name}, {Integer.MinValue} to {Integer.MaxValue}")
        Console.WriteLine($"Long    is System.{GetType(Long).Name}, {Long.MinValue} to {Long.MaxValue}")

        Dim anything As Object = 42
        Console.WriteLine($"Object holds {anything.GetType().Name}; CInt(anything) + 1 = {CInt(anything) + 1}")
        anything = "forty-two"
        Console.WriteLine($"Object now holds {anything.GetType().Name}")

        Dim first As BookRecord
        first.Title = "Dune"
        first.Copies = 3S
        first.Price = 9.99D
        Dim second = first
        second.Title = "Emma"
        Console.WriteLine($"Structure copy: first={first.Title}, second={second.Title}")

        Dim shelf1 As New Book With {.Title = "Dune"}
        Dim shelf2 = shelf1
        shelf2.Title = "Emma"
        Console.WriteLine($"Class reference, no Set: shelf1={shelf1.Title}, shelf2={shelf2.Title}")

        Dim copies = 3
        AddCopyByDefault(copies)
        Console.WriteLine($"After the default (ByVal) Sub: {copies}")
        AddCopyByRef(copies)
        Console.WriteLine($"After the ByRef Sub: {copies}")
    End Sub
End Module

Short   is System.Int16, -32768 to 32767
Integer is System.Int32, -2147483648 to 2147483647
Long    is System.Int64, -9223372036854775808 to 9223372036854775807
Object holds Int32; CInt(anything) + 1 = 43
Object now holds String
Structure copy: first=Dune, second=Emma
Class reference, no Set: shelf1=Emma, shelf2=Emma
After the default (ByVal) Sub: 3
After the ByRef Sub: 4

Private Function ParseCopies(text As String) As Long
    On Error GoTo Fail
    ParseCopies = CLng(text)
    Exit Function
Fail:
    Debug.Print "bad number: " & text
    ParseCopies = 0
End Function

Private Sub PrintReport()
    GoSub WriteHeader
    Debug.Print "body"
    Exit Sub
WriteHeader:
    Debug.Print "== Report =="
    Return
End Sub

Option Strict On

Imports System.Globalization

Module M02ErrorsAndSubroutines
    Function ParseCopies(text As String) As Integer
        Try
            Return Integer.Parse(text, CultureInfo.InvariantCulture)
        Catch ex As FormatException
            Console.WriteLine($"  FormatException for '{text}'")
            Return 0
        Catch ex As OverflowException
            Console.WriteLine($"  OverflowException for '{text}'")
            Return Integer.MaxValue
        Finally
            Console.WriteLine($"  checked '{text}'")
        End Try
    End Function

    Function FormatLine(title As String, copies As Integer) As String
        Return $"{title,-8}{copies,3}"
    End Function

    Sub PrintReport(titles As String(), copies As Integer())
        For i = 0 To titles.Length - 1
            Console.WriteLine(FormatLine(titles(i), copies(i)))
        Next
    End Sub

    Sub Main()
        Console.WriteLine(ParseCopies("4"))
        Console.WriteLine(ParseCopies("four"))
        Console.WriteLine(ParseCopies("99999999999"))

        Dim value As Integer
        If Integer.TryParse("12x", NumberStyles.Integer, CultureInfo.InvariantCulture, value) Then
            Console.WriteLine($"parsed {value}")
        Else
            Console.WriteLine("TryParse says no, and nothing was thrown")
        End If

        PrintReport({"Dune", "Emma"}, {3, 12})
    End Sub
End Module

  checked '4'
4
  FormatException for 'four'
  checked 'four'
0
  OverflowException for '99999999999'
  checked '99999999999'
2147483647
TryParse says no, and nothing was thrown
Dune      3
Emma     12

Dim n As Integer
n = FreeFile
Open "C:\temp\catalog.txt" For Output As #n
Print #n, "Dune,3"
Print #n, "Emma,12"
Close #n

Dim fso As Object
Set fso = CreateObject("Scripting.FileSystemObject")
If fso.FileExists("C:\temp\catalog.txt") Then
    Debug.Print fso.GetFile("C:\temp\catalog.txt").Size
End If

Option Strict On

Imports System.IO
Imports System.Text

Module M03Files
    Sub Main()
        Dim folder = Path.Combine(Path.GetTempPath(), "shelf-g6-" & Guid.NewGuid().ToString("N"))
        Directory.CreateDirectory(folder)
        Try
            Dim catalog = Path.Combine(folder, "catalog.txt")
            Dim utf8 As New UTF8Encoding(False)

            Using writer As New StreamWriter(catalog, False, utf8)
                writer.WriteLine("Dune,3")
                writer.WriteLine("Emma,12")
            End Using
            File.AppendAllText(catalog, "Ulysses,1" & vbLf, utf8)

            Using reader As New StreamReader(catalog, utf8)
                Do While Not reader.EndOfStream
                    Dim line = reader.ReadLine()
                    Console.WriteLine($"read: {line}")
                Loop
            End Using

            File.Copy(catalog, Path.Combine(folder, "backup.txt"))
            File.WriteAllText(Path.Combine(folder, "notes.md"), "# notes", utf8)

            For Each file In Directory.EnumerateFiles(folder, "*.txt").OrderBy(Function(p) p)
                Dim info As New FileInfo(file)
                Console.WriteLine($"{info.Name,-12}{info.Length,4} bytes")
            Next
            Console.WriteLine($"catalog.txt exists: {File.Exists(catalog)}, folder exists: {Directory.Exists(folder)}")
            Console.WriteLine($"extension: {Path.GetExtension(catalog)}, name without extension: {Path.GetFileNameWithoutExtension(catalog)}")
        Finally
            Directory.Delete(folder, True)
        End Try
        Console.WriteLine($"folder exists after cleanup: {Directory.Exists(folder)}")
    End Sub
End Module

read: Dune,3
read: Emma,12
read: Ulysses,1
backup.txt    25 bytes
catalog.txt   25 bytes
catalog.txt exists: True, folder exists: True
extension: .txt, name without extension: catalog
folder exists after cleanup: False

Dim stock
Set stock = CreateObject("Scripting.Dictionary")
stock.CompareMode = 1                   ' text comparison: keys ignore case
stock("Dune") = 3                       ' assignment adds the key
Dim copies
copies = stock("Ulysses")               ' reading a missing key ADDS it, with an empty value

Dim label
label = IIf(copies > 0, "in stock", "out of stock")      ' evaluates both branches

Dim summary
summary = "Dune: " & stock("Dune") & _
          ", copies: " & stock.Count & _
          ", label: " & label

Option Strict On

Module M04CollectionsAndExpressions
    Function Describe(copies As Integer) As String
        Return If(copies > 0, "in stock", "out of stock")
    End Function

    Sub Main()
        Dim stock As New Dictionary(Of String, Integer)(StringComparer.OrdinalIgnoreCase)
        stock("Dune") = 3
        stock.Add("Emma", 0)
        stock("DUNE") += 1

        For Each pair In stock
            Console.WriteLine($"{pair.Key,-6}{pair.Value,2}  {Describe(pair.Value)}")
        Next

        Dim copies As Integer
        If stock.TryGetValue("Ulysses", copies) Then
            Console.WriteLine(copies)
        Else
            Console.WriteLine("Ulysses is not in the dictionary")
        End If
        Try
            Console.WriteLine(stock("Ulysses"))
        Catch ex As KeyNotFoundException
            Console.WriteLine("Reading a missing key throws KeyNotFoundException")
        End Try

        Dim legacy As New Microsoft.VisualBasic.Collection()
        legacy.Add("Dune", "k1")
        legacy.Add("Emma", "k2")
        Console.WriteLine($"Collection(1)={legacy(1)}, Collection(""k2"")={legacy("k2")}, Count={legacy.Count}")
        Dim modern As New List(Of String) From {"Dune", "Emma"}
        Console.WriteLine($"List(0)={modern(0)}, Count={modern.Count}")

        Dim nickname As String = Nothing
        Console.WriteLine(If(nickname, "(no nickname)"))

        Dim summary = stock.
            Where(Function(p) p.Value > 0).
            Select(Function(p) p.Key.ToUpperInvariant()).
            ToList()
        Dim total = stock.Values.Sum() +
            modern.Count
        Console.WriteLine(String.Join(", ", summary) & " / total " & total.ToString())
    End Sub
End Module

Dune   4  in stock
Emma   0  out of stock
Ulysses is not in the dictionary
Reading a missing key throws KeyNotFoundException
Collection(1)=Dune, Collection("k2")=Emma, Count=2
List(0)=Dune, Count=2
(no nickname)
DUNE / total 6

Option Strict On

Imports System.IO

Public NotInheritable Class LogFile
    Implements IDisposable

    Private ReadOnly _writer As StreamWriter
    Private _disposed As Boolean

    Public Sub New(path As String)
        _writer = New StreamWriter(path, True)
    End Sub

    Public Sub WriteLine(text As String)
        ObjectDisposedException.ThrowIf(_disposed, Me)
        _writer.WriteLine(text)
    End Sub

    Public Sub Dispose() Implements IDisposable.Dispose
        If Not _disposed Then
            _disposed = True
            _writer.Dispose()
            Console.WriteLine("LogFile closed")
        End If
    End Sub
End Class

Module M10Disposal
    Sub Main()
        Dim path = IO.Path.Combine(IO.Path.GetTempPath(), "shelf-g6-log-" & Guid.NewGuid().ToString("N") & ".txt")
        Dim kept As LogFile
        Using log As New LogFile(path)
            kept = log
            log.WriteLine("first line")
            Console.WriteLine("inside Using")
        End Using
        Console.WriteLine($"after Using, file holds: {File.ReadAllText(path).Trim()}")
        Try
            kept.WriteLine("too late")
        Catch ex As ObjectDisposedException
            Console.WriteLine("writing after the block throws ObjectDisposedException")
        End Try
        File.Delete(path)
    End Sub
End Module

inside Using
LogFile closed
after Using, file holds: first line
writing after the block throws ObjectDisposedException