Destructor

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Destructor

Called automatically when a class or user defined type goes out of scope or is destroyed

Syntax

Type typename
field declarations
Declare Destructor ( )
End Type
Destructor typename ( ) [ Export ]
statements
End Destructor

Parameters

• typename

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 Statement 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 (but several destructors can be called in a chained way if the type contains or inherits other types with their own destructors).

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.

Remarks

Dialect Differences

• Object-related features are supported only in the -lang fb dialect.

Differences from QB

• New to FreeBASIC

See also

• Class
• Constructor
• Delete Statement
• Destructor (Module)
• Type

Examples

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

Output:

Creating: main.x
Creating: main.scope.x
Destroying: main.scope.x
Creating: A.x
Destroying: A.x
Destroying: main.x

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Category: User Defined Types
Kind: type

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.