Hello list. I need to implement lazy loading for an OPF so I need to intercept the read call to a property. Lets take the following classes:

    TClient = class
    private
      FName: string;
    published
      property Name: string read FName write FName;
    end;
    TInvoice = class
    private
      FClient: TClient;
    published
      property Client: TClient read FClient write FClient;
    end;

Tinvoice.Client need to be checked by the OPF before return its actual value.

Some approaches I have outlined so far:

1. A future aspect implementation: so I can verify the Client property just before the value is returned to the caller.

2. A future (if possible) proxy (like Java proxy) implementation: so the OPF can place a "fake" TClient instance in the client property, and intercept calls to the Client instance. Just like Hibernate actually do.

3. A proxy object between TInvoice and TClient is possible today, with some effort from the user:

    TInvoice = class
    private
      FClient: specialize TProxy<TClient>;
    published
      property Client: TClient read GetClient write SetClient;
    end;
    GetClient: Result := FClient.GetValue;
    SetClient: FClient.SetInstance(AValue);

4. Finally a manual check is also possible and it's currently my preferred approach, but also with some effort from the user:

    TInvoice = class
    private
      FClient: TClient;
    published
      property Client: TClient read GetClient write FClient;
    end;
    GetClient: somecheck(Self, @FClient); Result := FClient;

Is there some compiler magic I am missing?

Joao Morais

Joao Morais wrote

Is there some compiler magic I am missing?

Nope, you don't miss anything. The only thing which *could* help you is when the new RTTI unit is implemented which contains a TVirtualMethodInterceptor which allows you to - as its name suggests - intercept all calls to virtual methods, change their parameters, swallow or raise exceptions or discard the call completely. This will only work on virtual methods however (because this constructs a special VMT on the fly) and it might still take some time until this is implemented.

Regards,
Sven

Great new! Where do I click +1? =)

2.8 or pos 2.8 roadmap?

Joao Morais

My *hope* is to get it into the next major version (aka 2.8) together with the complete extended RTTI, but I don't promise anything, as I first need to work on generics.

Regards,
Sven