From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2006-02-13 11:02:54
Ion Gaztañaga wrote:
...
> I meant that with a class that wants to contain a pure-RAII object
> without dynamic allocation/optional, it has to initialize the object
> in
> the member constructor list. Imagine that depending constructor
> arguments and the constructed other member, you want to open,
> open_or_create or create a RAII object. Since you have to initialize
> raii in the initializer list, Iyou can only use a constructor type.
> And
> for example, to open raii I need 3 arguments, and to create raii
> resource I need 4.
>
> class Holder
> {
> RAII raii;
> public:
> Holder(/*some conditions*/)
> : raii(/*Create or open depending arguments,
> and other temporary results*/)
> {}
> };
>
> If I have two phase construction (error handling omitted):
>
> class Holder
> {
> TwoPhase twophase;
> public:
> Holder(/*some conditions*/)
> : raii()
> {
> /*Depending on passed conditions, open or create*/
> if()
> twophase.open(/*3 arguments*/)
> else
> twophase.create(/*4 arguments*/)
> //If we throw, the twophase destructor will free resources
> }
> };
Looking at this from the RAII perspective, I'd say, hmm, what if I have a
constructor that opens if the resource is already available, otherwise will
ask the OS for a new one. IIRC, that's what Microsoft does for named IPC
objects.
This simplifies the usage of the library from the user's perpective.
Jeff Flinn