Destructor
Called automatically when a class or user defined type goes out of scope or is destroyed
The destructor method is called when a user defined Type or Class variable goes out of scope or is destroyed explicitly with the Delete operator.
typename is the name of the type for which the Destructor method is declared and defined. Name resolution for typename follows the same rules as procedures when used in a Namespace.
The Destructor method is passed a hidden This parameter having the same type as typename.
The destructor in a type is called before the destructors on any of its fields. Therefore, all fields are accessible with the hidden This parameter in the destructor body.
Only one destructor may be declared and defined per type.
Since the End statement does not close any scope, object destructors will not automatically be called if the End statement is used to terminate the program.
Destructor can be also called directly from the typename instance like the other member methods (Sub) and with the same syntax, i.e. using a member access operator, e.g. obj.Destructor(). The object, and all its members, are assumed to be constructed and in a valid state, otherwise its effects are undefined and may cause crashes. This syntax is useful in cases where obj has been constructed manually, e.g. with obj.Constructor() or Placement New.
Output:
Syntax
Parameters
Description
The destructor method is called when a user defined Type or Class variable goes out of scope or is destroyed explicitly with the Delete operator.
typename is the name of the type for which the Destructor method is declared and defined. Name resolution for typename follows the same rules as procedures when used in a Namespace.
The Destructor method is passed a hidden This parameter having the same type as typename.
The destructor in a type is called before the destructors on any of its fields. Therefore, all fields are accessible with the hidden This parameter in the destructor body.
Only one destructor may be declared and defined per type.
Since the End statement does not close any scope, object destructors will not automatically be called if the End statement is used to terminate the program.
Destructor can be also called directly from the typename instance like the other member methods (Sub) and with the same syntax, i.e. using a member access operator, e.g. obj.Destructor(). The object, and all its members, are assumed to be constructed and in a valid state, otherwise its effects are undefined and may cause crashes. This syntax is useful in cases where obj has been constructed manually, e.g. with obj.Constructor() or Placement New.
Example
Type T
value As ZString * 32
Declare Constructor ( init_value As String )
Declare Destructor ()
End Type
Constructor T ( init_value As String )
value = init_value
Print "Creating: "; value
End Constructor
Destructor T ()
Print "Destroying: "; value
End Destructor
Sub MySub
Dim x As T = ("A.x")
End Sub
Dim x As T = ("main.x")
Scope
Dim x As T = ("main.scope.x")
End Scope
MySub
value As ZString * 32
Declare Constructor ( init_value As String )
Declare Destructor ()
End Type
Constructor T ( init_value As String )
value = init_value
Print "Creating: "; value
End Constructor
Destructor T ()
Print "Destroying: "; value
End Destructor
Sub MySub
Dim x As T = ("A.x")
End Sub
Dim x As T = ("main.x")
Scope
Dim x As T = ("main.scope.x")
End Scope
MySub
Output:
Creating: main.x Creating: main.scope.x Destroying: main.scope.x Creating: A.x Destroying: A.x Destroying: main.x
Dialect Differences
- Object-related features are supported only in the -lang fb dialect.
Differences from QB
- New to FreeBASIC
See also