STATIC (Member)
Declare a static member procedure or variable
Syntax:
Type typename
End Type
Dim typename.variablename As DataType [= initializer] [, ...]
[Static] Sub|Function typename.procedurename ...
End Type
Dim typename.variablename As DataType [= initializer] [, ...]
[Static] Sub|Function typename.procedurename ...
...
End Sub|FunctionDescription:
- Static member procedures
- Static member variables
Static methods do not have an implicit This instance argument passed to them. This allows them to be used like normal non-member procedures (for example with callback procedure pointers). An advantage of Static methods are that they are encapsulated in the typename namespace, and therefore have the ability to access the Private or Protected members or methods of instances of typename.
Static methods can be called directly anywhere in code, like normal non-member procedures, or on objects of type typename, similar to non-static methods, however either way there is no implicit or explicit This (or explicit Base (member access)) access possible from within a static method.
For member procedures with a Static declaration, Static may also be specified on the corresponding procedure bodies, for improved code readability.
Static methods can be called directly anywhere in code, like normal non-member procedures, or on objects of type typename, similar to non-static methods, however either way there is no implicit or explicit This (or explicit Base (member access)) access possible from within a static method.
For member procedures with a Static declaration, Static may also be specified on the corresponding procedure bodies, for improved code readability.
Static member variables are created and initialized only once independently of any object construction, in contrast to non-static ("instance") member variables which are created again and again for each separate object. Static members are always Shared, even if Shared was not specified in the declaration. Thus, Static member variables are similar to global variables, except that they are declared in a Type namespace.
Each Static member variable declared in a Type must be explicitly allocated somewhere outside the type by using a Dim statement. The declaration inside the Type is the prototype that is visible to every module seeing the Type declaration. The definition outside the Type allocates and optionally initializes the Static member variable. There can only be one definition per Static member variable: it can only be allocated in a single module, not in multiple ones. This is the same as for Extern variables.
A Static member variable is subject to member access control except for its definition outside the Type. If a private Static member variable is to be explicitly initialized outside the Type's member procedures, an initializer must be provided with the definition.
Each Static member variable declared in a Type must be explicitly allocated somewhere outside the type by using a Dim statement. The declaration inside the Type is the prototype that is visible to every module seeing the Type declaration. The definition outside the Type allocates and optionally initializes the Static member variable. There can only be one definition per Static member variable: it can only be allocated in a single module, not in multiple ones. This is the same as for Extern variables.
A Static member variable is subject to member access control except for its definition outside the Type. If a private Static member variable is to be explicitly initialized outside the Type's member procedures, an initializer must be provided with the definition.
Examples:
'' Example showing how the actual procedure invoked by a member can be set at runtime.
'' using static member procedures.
Type _Object
Enum handlertype
ht_default
ht_A
ht_B
End Enum
Declare Constructor( ByVal ht As handlertype = ht_default)
Declare Sub handler()
Private:
Declare Static Sub handler_default( ByRef obj As _Object )
Declare Static Sub handler_A( ByRef obj As _Object )
Declare Static Sub handler_B( ByRef obj As _Object )
handler_func As Sub( ByRef obj As _Object )
End Type
Constructor _Object( ByVal ht As handlertype )
Select Case ht
Case ht_A
handler_func = @_Object.handler_A
Case ht_B
handler_func = @_Object.handler_B
Case Else
handler_func = @_Object.handler_default
End Select
End Constructor
Sub _Object.handler()
handler_func(This)
End Sub
Sub _Object.handler_default( ByRef obj As _Object )
Print "Handling using default method"
End Sub
Sub _Object.handler_A( ByRef obj As _Object )
Print "Handling using method A"
End Sub
Sub _Object.handler_B( ByRef obj As _Object )
Print "Handling using method B"
End Sub
Dim objects(1 To 4) As _Object => _
{ _
_Object.handlertype.ht_B, _
_Object.handlertype.ht_default, _
_Object.handlertype.ht_A _
}
'' 4th array item will be _Object.handlertype.ht_default
For i As Integer = 1 To 4
Print i,
objects(i).handler()
Next i
'' using static member procedures.
Type _Object
Enum handlertype
ht_default
ht_A
ht_B
End Enum
Declare Constructor( ByVal ht As handlertype = ht_default)
Declare Sub handler()
Private:
Declare Static Sub handler_default( ByRef obj As _Object )
Declare Static Sub handler_A( ByRef obj As _Object )
Declare Static Sub handler_B( ByRef obj As _Object )
handler_func As Sub( ByRef obj As _Object )
End Type
Constructor _Object( ByVal ht As handlertype )
Select Case ht
Case ht_A
handler_func = @_Object.handler_A
Case ht_B
handler_func = @_Object.handler_B
Case Else
handler_func = @_Object.handler_default
End Select
End Constructor
Sub _Object.handler()
handler_func(This)
End Sub
Sub _Object.handler_default( ByRef obj As _Object )
Print "Handling using default method"
End Sub
Sub _Object.handler_A( ByRef obj As _Object )
Print "Handling using method A"
End Sub
Sub _Object.handler_B( ByRef obj As _Object )
Print "Handling using method B"
End Sub
Dim objects(1 To 4) As _Object => _
{ _
_Object.handlertype.ht_B, _
_Object.handlertype.ht_default, _
_Object.handlertype.ht_A _
}
'' 4th array item will be _Object.handlertype.ht_default
For i As Integer = 1 To 4
Print i,
objects(i).handler()
Next i
'' Assign an unique ID to every instance of a Type (ID incremented in order of creation)
Type UDT
Public:
Declare Property getID () As Integer
Declare Constructor ()
Private:
Dim As Integer ID
Static As Integer countID
End Type
Dim As Integer UDT.countID = 0
Property UDT.getID () As Integer
Property = This.ID
End Property
Constructor UDT ()
This.ID = UDT.countID
UDT.countID += 1
End Constructor
Dim As UDT uFirst
Dim As UDT uSecond
Dim As UDT uThird
Print uFirst.getID
Print uSecond.getID
Print uThird.getID
Type UDT
Public:
Declare Property getID () As Integer
Declare Constructor ()
Private:
Dim As Integer ID
Static As Integer countID
End Type
Dim As Integer UDT.countID = 0
Property UDT.getID () As Integer
Property = This.ID
End Property
Constructor UDT ()
This.ID = UDT.countID
UDT.countID += 1
End Constructor
Dim As UDT uFirst
Dim As UDT uSecond
Dim As UDT uThird
Print uFirst.getID
Print uSecond.getID
Print uThird.getID
Differences from QB:
- New to FreeBASIC
See also:
Back to Procedures
Back to User Defined Types
