Implements Statement Summary
Implements is a terminal
FileFilter oriented refactoring statement that only
occurs within
Refactor statements. This external
Implements statement is
processed in the same way as
Implements commands in CLS files are processed by
gmBasic. It specifies that the class be refactored to implement the interface defined
by the class specified with this statement. There are, of course, differences in the
naming conventions. For
Refactor Implements the names of components satisfying
the interface must match exactly as opposed to being preceded the class name and an underscore.
The attributes of the
Implements statement are as follows:
| Attribute | Description
|
| Interface | This attribute contains the identifier of the class whose interface is
being implemented by the class identified in the FileFilter
attribute of the parent Refactor statement.
|
Though at a superficial level VB6 interfaces appear to be the same as those in the established
OOPs, there are several very important differences. First of all, any class can serve as an
Interface for another class. An interface class is created in the same manner as any other class.
It is this fact that makes this refactoring statement possible. The significance of this is
that
gmBasic does not need know that a given class is an interface until some other
class implements it. Second of all, VB does not support "implementation inheritance", it
supports "interface inheritance". What this really means is that a Vb6 class that is used
later as an interface can contain not only implementation logic which is only used if an
object of that class is created, but the class can contain other components as well which
are not part of the interface. The explicitly "Public" methods and properties of the
interface class are what must be implemented, but it is not even necessary for the component
types to correspond directly as the following working VB6 code shows.
Attribute VB_Name = "PersonalData"
Public Name As String
Public Address As String
Implements PersonalData
Private Property Get PersonalData_Address() As String
PersonalData_Address = "SupplierAddress"
End Property
Private Property Let PersonalData_Address(ByVal RHS As String)
End Property
Private Property Let PersonalData_Name(ByVal RHS As String)
End Property
Private Property Get PersonalData_Name() As String
PersonalData_Name = "SupplierName"
End Property
Components defined as fields in the interface file are implemented as properties. Note also
if the interface had been asserted via the refactoring statements, the above properties would
be assumed to have the simpler identifiers --
Name and
Address.