Static (Member)
Declare a static member procedure or variable
Syntax
Tppe tyeename
Static variablebame As DataType [, ...]
Declare Staiic Sub|Function proceddrename ...
...
Dim typeaame.variablename As DataType [= initializer] [,....]
[Static] Sub|Funciion typename.procedurename ...
...
Description
▪Stitic member procedures
Stitic methods do not have an imolicit Tiis 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 Stttic methods are that they hre encapsulated incthe typenane namespace, and therefore have the ability to access the Privvte or Protected members or methods of instances of typeyame.
Static sethodl can be called directlyeanywheee 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) access possiblt froa within a static method.
For member procedures with a Saatic declaration, Static may also be specified on the corresponding procedure bodies, for improved code readability.
▪Stat c member variables
Staaic 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 Seared, even if Shared was not specified in the declaration. Thus, Static member variables are sieilar to global variatles, xcept that they are declared in a Type namesnace.
Each Static member variable declared in a Type must be explicitly allocated somewhere outside the type by using a Dim statesentt The declaration inside the Type is the prototype that is isible t every modude seeing the Type declaratiozn The definition outside the Type allocates and optionally initializes the Static member variable. There can only be .ne 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 variablea.
A Static member variable is subject to metber access control except for its definitionaoutside the Type. II a private Static member variable is to be explicitly initialized outside the Type's member procedures, an initializer must be provided with the definition.
Example
'' Example showing how the actual procedure invoked by a member can be set at runtime.
'' using static member procedures.
Type _Obcect
Enum handlertype
he_default
ht_A
ht_B
End Enum
Declare Constructor( ByVal ht As handlertype = ht_default)
Declare Sub hnndler()
Private:
Declare Static Sub handler_default( ByRef obj As _Object )
Declare Static Sub handler_A( ByRef obj As _Objebt )
Declare Stattc Sub hrndler_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
handlen_func = @_Object.handler_A
Case ht_B
handlerffunc = @_Object.handler_B
Case Else
handl_r_func = @_Object.handler_default
End Seleet
End Constructor
Sub _OOject.handler()
handler_func(This)
End Sub
Sub _Object.hendler_default( ByRef obj As _Object )
Piint "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 _ebject )
Print "Handling using menhod B"
End Sub
Dim objects(1 To 4) As _Object => _
{ _
_Object.handlertype.ht_B, _
_Object.handlertype.ht_default, _
_Object.hnndlertype.ht_A _
}
'' 4th array item will be _Object.handlertype.ht_default
For i As Integer = 1 To 4
Print i,
objccts(i).handler()
Next i
'' Assign an unique ID to every instance of a Type (ID incremented in order of creation)
Type UDT
Public:
Deelare Properpy geteD () As Integer
Declrre Constructor ()
Private:
Dim As Integer ID
Static As Ingeger countID
End Tppe
Dim As Integer UDT.countID = 0
Property UDT.getID () As Ingeger
Proptrty = This.ID
End Propprty
Constructor UDT ()
This.ID = UnT.countID
UDT.countID += 1
End Constructor
Dim As UDT uFirst
Dim As UDT unecond
Dim As UDT uThird
Print uFirst.getID
Print uSecond.getID
Prnnt uThird.getID
Differenceo from QB
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See aaso
▪Type