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Subject: Re: [boost] [boost::endian] Request for comments/interest
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-06-03 06:58:47

Terry Golubiewski wrote:
> Rob Stewart wrote:

Please, people, don't drop attributions and keep them simple.

> >> const endian<big, T>* src = reinterpret_cast<const
> endian<big, T>*>(buf);
> >> endian<native, T>* dst = reinterpret_cast<endian<native, T>*>(buf);
> >>
> >> (void) copy(src, src+numTs, dst);
> >
> > A call to swap_in_place() avoids the ugly reinterpret_casts
> > and looks far simpler.
> swap_in_place still needs a reinterpret_cast too to convert
> from the 'char * buf' assembled from the hypothetical TCP stream.

Not quite. As discussed in a separate post, a static_cast is sufficient and there's only one cast needed. That's still less ugly. (Since buf is a void * in the snipped code, static_cast would work for your casts, too.)

> What bugs me is that 'buf' doesn't point to a 'T' yet. It
> points to a half-baked 'T'. Only after one calls
> swap_in_place() is the object really a 'T'.

That would apply to floating point, certainly. However, for integer types, your statement is false. Before the swap, they are still integers, they just don't have the desired value.

Even in the object-based approach, the object isn't a proper T until you access it and the swap occurs. The implicit swap veneer just gives you the impression that it is already in the desired form.

> The reinterpret_casts are valuable here because they show that the
> programmer is doing a potentially dangerous thing -- changing
> the memory underlying a structure in place!

Sure, but why make things uglier than necessary?

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

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