Friend

Makes a member of a class available to the whole project, and keeps it out of the class’s public interface.

Syntax:

Friend [ Static ] [ Overridable ] Sub | Function | Property Get | Property Let | Property Set name …
Friend [ ReadOnly | WithEvents ] varname [ As [ New ] type ] [ = value ] [ , varname … ]

In a procedure declaration, Friend takes the place of Public, Private or Protected. The rest of the declaration is described on the Sub, Function and Property pages.

Every module and class of the project can use a Friend member, through a variable of the class’s own type. The class does not publish it: the type library of an ActiveX DLL lists no Friend procedure or variable. Use Friend for what the classes of a project need from one another, and that a client of the class should not call.

Note BETA 1034

A Friend member also answers late-bound calls, through an Object or Variant variable and through CallByName, because the compiler’s IDispatch finds it. This holds for an object passed to another project too, so that project can call its Friend procedures and read and write its Friend variables. VB6 raises error 438, as twinBASIC does for a Private member. Do not rely on Friend to keep a member away from code outside the project.

Note BETA 1034

A project that references a package can use the Friend members of the package’s classes, as if they were Public.

Note BETA 1034

The first Friend after a Delegate statement is refused with TB5182, Syntax error. No handler for this symbol, even though nothing is wrong with it. Move the Delegate to the end of the class. The Delegate page says what else this affects.

Where it can be used

Friend applies to the members of a class, and a form is a class too.

Member of a class	Result
Sub, Function, Property Get, Property Let, Property Set, Sub New	Allowed.
Variable	Allowed, under the rules for a Public variable. It can have an initial value, or be ReadOnly or WithEvents. A fixed-size array is refused, with TB5131.
Event, Enum, Type	Allowed, and the same as Public: the type library lists them.
Const	Refused, with TB5250: Constants in a class cannot be Public.
Declare, Delegate	Refused, with TB5227: these must be Private in a class.

Anywhere else Friend is a syntax error, TB5182: on a member of a Module, an Interface or a Type, and on a Class, Module or Interface itself. It is refused inside a procedure as well.

A declaration has one access modifier, so Public Friend Sub and Protected Friend Sub are syntax errors. Static and Overridable can stand on either side of Friend.

Note

VB6 allows Friend only on a Sub, Function or Property procedure of a class. On anything else in a class it reports Expected: Sub or Function or Property, and in a standard module Only valid in object module. Friend on a variable, Event, Enum or Type is a twinBASIC extension.

Private types in a signature

In VB6, a Private Type or Enum can be a parameter or the return type of a Friend procedure, but not of a Public one. That is a common reason to use Friend there. twinBASIC allows these types in both, in an ActiveX DLL too. The difference is in the type library: a Public member that uses a Private type adds that type to it, and a Friend member does not.

Implements, Inherits and Via

A class that Implements another class does not have to provide its Friend procedures. Calling one through a variable of the implemented class, on an object of the implementing class, raises error 97, Can not call friend function on object which is not an instance of defining class, as it does in VB6. A Friend variable is different: the implementing class must provide it, as a Property Get and a Property Let.

Warning BETA 1034

In a 32-bit build, that call damages the stack unless the procedure’s arguments and return value take exactly one stack slot besides Me. It raises error 97 correctly from a Sub with one argument of 4 bytes or less, from a Function or Property Get with no arguments, and from a Property Let with one such value. Any other signature, such as Function F(ByVal X As Long) As Long, a Sub with two arguments or a Sub with a ByVal Currency argument, ends an exe with an access violation before a handler runs, and a run in the IDE does not return. A Sub with no arguments raises an error 97 that On Error does not keep: in an exe the handler runs, and then the program stops with an error box when the procedure returns. A 64-bit build is not affected. Do not call a Friend procedure on an object that may be of an implementing class.

A class that Inherits another class inherits its Friend members, and they stay available to the whole project. A Friend Overridable procedure is overridden in the usual way.

Implements ... Via forwards the Friend members of the delegate as well as the Public ones, so they can be called on the delegating class from anywhere in the project. The ImplementsViaPrivateFriendlies attribute keeps them inside that class.

Example

Post changes the balance. Bank, in the same project, can call it, and a client of the class sees only Balance.

Class Account
    Private mBalance As Long

    Public Property Get Balance() As Long
        Balance = mBalance
    End Property

    ' For the rest of the project, not for clients of the class.
    Friend Sub Post(ByVal Amount As Long)
        mBalance = mBalance + Amount
    End Sub
End Class

Class Bank
    Public Function OpenAccount(ByVal Deposit As Long) As Account
        Set OpenAccount = New Account
        OpenAccount.Post Deposit
    End Function
End Class

Dim b As New Bank
Dim a As Account
Set a = b.OpenAccount(100)
a.Post 25
Debug.Print a.Balance    ' 125

A class that implements Account provides Balance, and has no Post to call:

Class TestAccount
    Implements Account

    Private Property Get Account_Balance() As Long
        Account_Balance = 1
    End Property
End Class

Dim a As Account
Set a = New TestAccount
Debug.Print a.Balance    ' 1
On Error Resume Next
a.Post 5
Debug.Print Err.Number   ' 97

Friend

Where it can be used

Private types in a signature

Implements, Inherits and Via

Example

See Also