Re: [Spirit-general] fusion adapted struct, compile error due to evil expectation operator - why? (minimal example provided)

[Joel de G. <jo...@bo...>]

On 1/30/2010 5:36 AM, Mat...@gm... wrote:
> Hi,
>
> I get a compiler error for this code which appears to be correct:
>
[...]
> I can see why the second works, but my (very limited) understanding of Spirit is that the first one should also work.
> What's going on?

It seems to be a precedence or grouping problem. Putting some of the code
in parens fixes it:

     =   name
             >> attr(DCurrentDepSource::Current)
             >> (qi::repeat(2)[node]
             > name
             >> attr(DCurrentDepSource::Gain)
             >> +eol);

I think this is a major gotcha that should be documented. It has
to do with flattening of the sequences. Your original code
has this grouping:

     (a >> b) > (c >> d >> e) // > has a lower precendence than >>

while the fix has this:

     a >> (b > (c >> d >> e))

It's very subtle and should be studied well and documented.

Regards,
-- 
Joel de Guzman
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