BASE (initializer)
Specifies an initializer for the base UDT in derived UDT constructors
Syntax:
base ( constructor-parameters... )
or:
base ( UDT-initializers... )
Description:
The Base initializer can be used at the top of constructors of derived UDTs. It allows to specify an explicit constructor call or UDT initializers to be used to initialize the base object. It will replace the implicit default initialization, and must appear above any other statements in the constructor it is used in.
Note: Unlike "Base( )", a "Base (member access).Constructor( )" statement does not replace the implicit default initialization done by the constructor of a derived UDT, and can usually not be used legally, because it would result in two constructor calls for the base object (for an inheritance structure extending the built-in Object type, this second base constructor call may also corrupt the vtable pointer to point to the base-type vtable instead of to the type vtable).
Note: Unlike "Base( )", a "Base (member access).Constructor( )" statement does not replace the implicit default initialization done by the constructor of a derived UDT, and can usually not be used legally, because it would result in two constructor calls for the base object (for an inheritance structure extending the built-in Object type, this second base constructor call may also corrupt the vtable pointer to point to the base-type vtable instead of to the type vtable).
Examples:
Type SimpleParent
As Integer a, b, c
End Type
Type Child extends SimpleParent
Declare Constructor( )
End Type
Constructor Child( )
'' Simple UDT initializer
Base( 1, 2, 3 )
End Constructor
As Integer a, b, c
End Type
Type Child extends SimpleParent
Declare Constructor( )
End Type
Constructor Child( )
'' Simple UDT initializer
Base( 1, 2, 3 )
End Constructor
Type ComplexParent
As Integer i
Declare Constructor( ByVal As Integer = 0 )
End Type
Constructor ComplexParent( ByVal i As Integer = 0 )
This.i = i
End Constructor
Type Child extends ComplexParent
Declare Constructor( )
Declare Constructor( ByRef As Child )
End Type
Constructor Child( )
'' Base UDT constructor call
Base( 1 )
End Constructor
Constructor Child( ByRef rhs As Child )
'' Base UDT constructor call
Base( rhs.i )
End Constructor
As Integer i
Declare Constructor( ByVal As Integer = 0 )
End Type
Constructor ComplexParent( ByVal i As Integer = 0 )
This.i = i
End Constructor
Type Child extends ComplexParent
Declare Constructor( )
Declare Constructor( ByRef As Child )
End Type
Constructor Child( )
'' Base UDT constructor call
Base( 1 )
End Constructor
Constructor Child( ByRef rhs As Child )
'' Base UDT constructor call
Base( rhs.i )
End Constructor
Dialect Differences:
- Methods are only supported in the -lang fb dialect, hence Base has no function in other dialects.
Differences from QB:
- New to FreeBASIC
See also:
Back to User Defined Types
