Re: Interfaces in C++
On Oct 7, 10:46 am, "Chris Becke" <chris.be...@gmail.com> wrote:
You cant do that. On many platforms interfaces are a binary
interop used and supported by languages other than c++.
In which case, you must declare them ``extern "whatever"'', and
obey the contraints of that language. Or use some external
language (e.g. Corba) to define them. That's a completely
different problem, and largely irrelevant for most uses.
In order to interop however, the vtable for the interface MUST
be contiguous.
That depends entirely on the other language(s). In most cases,
you can't use virtual functions at all, without some sort of
intermediate code.
Clearly if you are working in a ahomogonous c++ only
environment you can use virtual like that. But, despite the
c++ standards body being unwilling to acknoledge it, c++
vtables *are* used for binary interop rendering this keyword
worse than useless.
That is, of course, complete bullshit. *IF* you're writing to
some other language, then obviously, you have to respect the
contraints of that language, and work with a common subset.
(The most frequent case of this is, of course, C, since almost
all operating systems today define their API in C.) But except
for the OS API, that's really a rare case, and certainly not
something that most developers (or the standards committee)
need to take into consideration. (Also, FWIW: virtual
inheritance was around long before the standard.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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