Re: [Boost-users] Tuple use/overuse? 2

From: gast128 (gast128_at_[hidden])
Date: 2007-07-26 04:33:04

Joel de Guzman <joel <at> boost-consulting.com> writes:

> 
> > - bind expression with tuple becomes a nightmare
> 
> Why? Ah access to the members?

Yes. boost::bind(&tp::get<1>, _1) does not work (something to do with bind's 
difficulties with overloads and return types?). This can be overcome by using 
Karlsson's tuple_select.

> 
> > - default initialising of its members is m_member() (while sometimes we 
> > reserve -1 for uninitialised)
> 
> Dunno what you mean. Please elaborate.

Oh this simple. Let says one has a tuple with handles boost::tuple<HANDLE>; In 
Win32 an INVALID_HANDLE_VALUE is defined as -1. So if one writes:

boost::tuple<HANDLE> tp;

If at the moment of definition, the actual values are not known, it should be 
default intialised with invalid handles (-1) and not with zeros, which can 
represent valid file handles. This can of course be overcome with an extra 
intialiser e.g.

const boost::tuple<HANDLE> g_tpInvalid(INVALID_HANDLE_VALUE);

and then always write:

boost::tuple<HANDLE> tp = tpInvalid;

but this is an extra step. Using a structure one could handle that in the 
defualt constructor.

Wkr,
me