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Subject: Re: [boost] [Polygon] review - isotropy.hpp
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-31 11:13:23

Simonson, Lucanus J
> Stewart, Robert wrote:
> > Simonson, Lucanus J wrote:
> >> Steven Watanabe wrote:
> >>
> >>> isotropy.hpp:308
> >>> What does y_c_edist mean, and why are you including a
> >>> constant in the gtl_and for euclidean_distance?
> >>
> >> This is a compiler workaround for MSVC8. There are a large
> >> number of them, unfortuantely. It is named with a mangling
> >> scheme related to the concept and function name that uses it.
> >> MSVC8 has two different code paths for instantiating
> >> templates and applying SFINAE. The one where it recognizes
> >> that it has seen a subtemplate before is incorrect and I used
> >> these constant types that are unique to each function to
> >> force MSVC8 to SFINAE correctly. I could perhaps put a
> >>
> >> //MSVC8 workaround
> >>
> >> on each one so that it doesn't cause too much confusion.
> >
> > (Caveat: I'm only responding to what I read here: I haven't
> looked at
> > the code in question. I may be way off the mark.)
> >
> > How about introducing a macro taking a constant argument, that
> > evaluates to the supplied constant, plus required punctuation, for
> > MSVC8 and to nothing for other compilers? That would make the code
> > self documenting and eliminate any #ifdef's where used.
> >
> The constant needs to be a unique type in each instance that
> the workaround is used. Also, there are no ifdefs used for
> this workaround because the code is legal in all compilers.

Fair enough. However, allow me two points. First, the unique type can be produced from the constant supplied to the macro. Second, one day you might actually drop support for MSVC8 and removing the invocation of a macro that you can search for easily, would make quick work of reverting to the syntax you wanted all along.

Thus, the macro can inject the extra type for MSVC8 only, leaving other compilers with the simpler code, which probably means reduced compilation time; the macro documents that the extra type is for MSVC8 only; and you have an easier way to remove the noise later.

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

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