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   ► KBTo/From GuidesASP Classic  Print This     

Destructor (ASP Classic and Delphi Prism Cross Reference Guide)

By Mike Prestwood

ASP Classic versus Delphi Prism: A side by side comparison between ASP Classic and Delphi Prism.

 
OOP Details
 

More object oriented (OO) stuff.

Destructor

[Other Languages] 

General Info: Class Destructor

A special class method called when an object instance of a class is destroyed. With some languages they are called when the object instance goes out of scope, with some languages you specifically have to call the destructor in code to destroy the object, and others use a garbage collector to dispose of object instances at specific times.

Desctructors are commonly used to free the object instance but with languages that have a garbage collector object instances are disposed of when appropriate. Either way, destructors or their equivalent are commonly used to free up resources allocated in the class constructor.

Languages Focus

Are object instances freed with a garbage collector? Or, do you have to destroy object instances.

ASP Classic:   Class_Terminate

When an object instance is destroyed, ASP calls a special parameter-less sub named Class_Terminate. For example, when the variable falls out of scope. Since you cannot specify parameters for this sub, you also cannot overload it.

To explicitly destroy an object, use Set YourClass = nothing. If the Class object is explicitly destroyed, the client returns with the script engine error details.

When an object instance is created from a class, ASP calls a special sub called Class_Initialize.

Syntax Example:
Class Cyborg
  Public Sub Class_Terminate
    Response.Write "<br>Class destroyed"
End Sub
End Class
Delphi Prism:  "Finalizer" finalize()

Unlike Delphi, Delphi Prism uses the .Net garbage collector to free managed object instances. Prism does not have nor need a true destructor.

In .Net, a finalizer is used to free non-managed objects such as a file or network resource. In Prism, you use the keyword finalizer to indicate the method is a finalizer. Each class can implement one and only one finalizer with a method name of finalize(), which is the method name used in Java and VB.Net.

Because you don't know when the garbage collector will call your finalizer, For non-managed resources, Microsoft recommends you implement the IDisposable interface and call it's Dispose() method at the appropriate time.

Syntax Example:
type
  Cyborg = class(IDisposable)
  private
    disposed: Boolean;
    method Dispose(disposing: Boolean);
  public
    method Dispose;
    finalizer Finalize;
  end;












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