Program Structure and Code Conventions

Option Strict On

Imports System.Reflection

Class DefaultType
    Dim plainField As Integer
    Const Limit As Integer = 3
    Sub DoWork()
    End Sub
    Function Compute() As Integer
        Return 1
    End Function
    Property Name As String
    Event Changed As EventHandler
    Sub New()
    End Sub
End Class

Structure DefaultStructure
    Dim plainField As Integer
    Sub DoWork()
    End Sub
End Structure

Module DefaultModule
    Dim plainField As Integer
    Sub DoWork()
    End Sub
End Module

Interface IDefault
    Sub DoWork()
End Interface

Enum DefaultEnum
    First
End Enum

Class [MyClass]
End Class

Module Program
    Private Function Access(info As MethodBase) As String
        If info.IsPublic Then Return "Public"
        If info.IsPrivate Then Return "Private"
        If info.IsAssembly Then Return "Friend"
        If info.IsFamily Then Return "Protected"
        Return "other"
    End Function

    Private Function TypeAccess(t As Type) As String
        Return If(t.IsPublic, "Public", If(t.IsNotPublic, "Friend", "nested"))
    End Function

    Private Sub Dump(t As Type)
        Console.WriteLine(t.Name & " -> " & TypeAccess(t))
        Const all As BindingFlags = BindingFlags.Instance Or BindingFlags.Static Or BindingFlags.Public Or BindingFlags.NonPublic Or BindingFlags.DeclaredOnly
        For Each f In t.GetFields(all)
            Dim kind = If(f.IsLiteral, "constant", "field")
            Dim vis = If(f.IsPublic, "Public", If(f.IsPrivate, "Private", If(f.IsAssembly, "Friend", "other")))
            Console.WriteLine("    " & kind & " " & f.Name & " = " & vis)
        Next
        For Each m In t.GetMethods(all)
            Console.WriteLine("    " & If(m.IsSpecialName, "accessor", "method") & " " & m.Name & " = " & Access(m))
        Next
        For Each c In t.GetConstructors(all)
            Console.WriteLine("    constructor = " & Access(c))
        Next
    End Sub

    Sub Main()
        Dump(GetType(DefaultType))
        Dump(GetType(DefaultStructure))
        Dump(GetType(DefaultModule))
        Console.WriteLine(GetType(IDefault).Name & " -> " & TypeAccess(GetType(IDefault)))
        Console.WriteLine(GetType(DefaultEnum).Name & " -> " & TypeAccess(GetType(DefaultEnum)))
        Console.WriteLine(GetType([MyClass]).Name)
    End Sub
End Module

DefaultType -> Friend
    field plainField = Private
    field _Name = Private
    field ChangedEvent = Private
    constant Limit = Private
    method DoWork = Public
    method Compute = Public
    accessor get_Name = Public
    accessor set_Name = Public
    accessor add_Changed = Public
    accessor remove_Changed = Public
    constructor = Public
DefaultStructure -> Friend
    field plainField = Public
    method DoWork = Public
DefaultModule -> Friend
    field plainField = Private
    method DoWork = Public
IDefault -> Friend
DefaultEnum -> Friend
MyClass

Option Strict On

Public NotInheritable Class Launcher
    Private Sub New()
    End Sub

    ' In a class, Main must be Shared. In a Module it would not need the keyword.
    Public Shared Function Main(args As String()) As Integer
        Console.WriteLine("entry point: " & GetType(Launcher).FullName)
        Console.WriteLine("exit code requested: " & Exitcode(args).ToString())
        Return Exitcode(args)
    End Function

    Private Shared Function Exitcode(args As String()) As Integer
        Return If(args.Length = 0, 0, 64)
    End Function
End Class

entry point: Shelf.Launcher
exit code requested: 0

Option Strict On

Module Importer
    Sub Main()
        Console.WriteLine("importer")
    End Sub
End Module

Module Reporter
    Sub Main()
        Console.WriteLine("reporter")
    End Sub
End Module

vbc : error BC30738: 'Sub Main' is declared more than once in 'TwoMains': TwoMains.Importer.Main(), TwoMains.Reporter.Main()
vbc : error BC30737: No accessible 'Main' method with an appropriate signature was found in 'AsyncMain'.
vbc : error BC30420: 'Sub Main' was not found in 'NoEntry'.
vbc : error BC30737: No accessible 'Main' method with an appropriate signature was found in 'InstanceMain'.

<StartupObject>Shelf.Reporter</StartupObject>

reporter

Option Strict On

Imports System.Collections.Generic
Imports System.Linq

Module Program
    Private Function [Select](items As IEnumerable(Of String), [Class] As String) As IEnumerable(Of String)
        Return items.Where(Function(item) item.StartsWith([Class], StringComparison.Ordinal))
    End Function

    Sub Main()
        ' Identifiers are case-insensitive; the declared spelling is what tooling displays.
        Dim shelfCount As Integer = 3
        SHELFCOUNT += 1
        Console.WriteLine("shelfCount = " & ShelfCount.ToString())
        console.writeline("this also compiles")

        ' Unicode letters are legal in identifiers, and so is a leading underscore plus a letter.
        Dim año As Integer = 2026
        Dim _draft As String = "v1"
        Console.WriteLine(año.ToString() & " " & _draft)

        ' A reserved word can be used as a name when it is escaped with square brackets.
        Dim [Loop] As String = "ring"
        Dim titles As String() = {"Dune", "Dubliners", "Emma"}
        Console.WriteLine([Loop] & ": " & String.Join(", ", [Select](titles, "Du")))

        ' Implicit line continuation: after a comma, an operator, an open bracket and
        ' before a close bracket, and before and after a query operator.
        Dim summary = String.Join(
            ", ",
            titles.Where(Function(t) t.Length > 4
                         ).OrderBy(Function(t) t))
        Dim total = shelfCount +
            2 *
            5
        Dim longTitles = From t In titles
                         Where t.Length > 4
                         Order By t Descending
                         Select t
        Console.WriteLine(summary & " | " & total.ToString() & " | " & String.Join("+", longTitles))

        ' Explicit continuation with _ ; since Visual Basic 16 a comment may follow it.
        Dim padded = "[" & _ ' the opening bracket
            titles(0).PadRight(8) & _ ' the title
            "]"
        Console.WriteLine(padded)

        ' Several statements on a physical line: legal, but Microsoft's conventions say not to.
        Dim x As Integer = 1 : Dim y As Integer = 2 : x += y
        Console.WriteLine("x = " & x.ToString())

        REM Old-style comment; the keyword REM works only at the start of a statement.
        Dim attempts As Integer = 0
Retry:
        attempts += 1
        If attempts < 3 Then GoTo Retry
        Console.WriteLine("attempts = " & attempts.ToString())
    End Sub
End Module

shelfCount = 4
this also compiles
2026 v1
ring: Dune, Dubliners
Dubliners | 14 | Dubliners
[Dune    ]
x = 3
attempts = 3

Option Strict On
Option Infer On

Imports System.Text

Namespace Lending
    Public Interface ILendable
        ReadOnly Property IsAvailable As Boolean
        Sub Lend(borrower As String)
    End Interface

    Public Class OverdueEventArgs
        Inherits EventArgs

        Public ReadOnly Property DaysLate As Integer

        Public Sub New(daysLate As Integer)
            Me.DaysLate = daysLate
        End Sub
    End Class

    Public Class Loan
        Implements ILendable

#Region "State"
        Private ReadOnly _title As String
        Private _borrower As String
        Private _overdueDays As Integer
#End Region

        Public Event Overdue As EventHandler(Of OverdueEventArgs)

        Public Sub New(title As String)
            _title = title
        End Sub

        Public ReadOnly Property IsAvailable As Boolean Implements ILendable.IsAvailable
            Get
                Return _borrower Is Nothing
            End Get
        End Property

        Public Sub Lend(borrower As String) Implements ILendable.Lend
            _borrower = borrower
        End Sub

        Public Sub MarkLate(days As Integer)
            _overdueDays = days
            RaiseEvent Overdue(Me, New OverdueEventArgs(days))
        End Sub

        Public Function Describe() As String
            Dim state = If(IsAvailable, "available", $"lent to {_borrower}")
            Return $"{_title}: {state}"
        End Function
    End Class

    Public Class Reminder
        Public Property Prefix As String = "Reminder"
        Public Property Sent As Integer
    End Class
End Namespace

Module Program
    Private WithEvents CurrentLoan As Lending.Loan

    ' Relaxed delegate: a Handles method may leave out the sender and e parameters.
    Private Sub OnOverdue() Handles CurrentLoan.Overdue
        Console.WriteLine("overdue handler ran")
    End Sub

    Sub Main()
        CurrentLoan = New Lending.Loan("Dune")
        Dim loan = CurrentLoan
        Console.WriteLine(loan.Describe())
        loan.Lend("Ana")
        Console.WriteLine(loan.Describe())

        loan.MarkLate(3)

        Dim reminder As New Lending.Reminder With {.Prefix = "Overdue notice"}
        With reminder
            .Sent += 1
            Console.WriteLine($"{.Prefix}: {.Sent} sent")
        End With

        Dim titles As String() = {"Dune", "Emma", "Ulysses"}
        Dim builder As New StringBuilder()
        For Each title In titles
            builder.Append(title).Append(";"c)
        Next
        Console.WriteLine(builder.ToString())

        If loan IsNot Nothing AndAlso Not loan.IsAvailable Then
            Console.WriteLine("still on loan")
        End If
    End Sub
End Module

Dune: available
Dune: lent to Ana
overdue handler ran
Overdue notice: 1 sent
Dune;Emma;Ulysses;
still on loan