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Subject: Re: [boost] Interest in a simple buffer abstraction?
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-01-28 09:24:39

Boris Kolpackov wrote:
> "Stewart, Robert" <Robert.Stewart_at_[hidden]> writes:
> > > std::vector<char> data_store_;
> > > boost::buffer data_;
> >
> > Why would you have both?
> Because I want the packet to own the data and to be able to access
> it using a natural interface. With your approach I would have to
> write gratuitous code like this.

No you wouldn't. As I showed in the portion of my reply that you cut, if your packet owns its data, then it would have a container of that data. The point of my idea is that you can create a packet type that *doesn't* own the data or even know how the data is stored because the adaptor would abstract the underlying storage type and provide a useful interface permitting the packet to append, copy, etc.

I understand that your idea is for a type that owns the data. I'm proposing an alternative view of the problem.

> > which requires that some other code create a std::vector<char> or
> > other container for the packet to use.
> This goes down the slippery slop of someone else owning the memory
> and making sure it is not gone while other objects still reference
> it.

When you want performance, you don't want to copy data. Your model requires that the data be copied. Mine references data allocated elsewhere. As I noted, that does indeed mean that the reference mustn't outlive the allocation, but with that responsibility comes improved performance and greater flexibility.

> If that's the functionality you want, then why bother with the
> buffer class at all? Simply store a pair: const void*, size_t; it
> will be just as convenient.

As I noted (in what you snipped), the adaptor type can still provide the additional functionality you had proposed: appending, copying, etc. You get none of that with such a pair.

When sharing a buffer among libraries, using my suggestion, memory need only be allocated in one place whilst various functions from different libraries can all reference that memory using a type-erased, feature rich, standardized reference to it.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP

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