On 7/21/2010 3:51 PM, Christophe Henry wrote:
>> I was getting my A's and B's mixed up, and you're getting your A's and
>> trees mixed up. What you want is:
>>
>> struct B
>> : or_<
>> when< comma< B, B >, fold_tree<..as before..> >
>> , when< A, mpl::vector1<A>() >
>> >
>> {};
>
> Argh!!! *Grumble* *Grumble*
> This is exactly the first solution I came up with (and spent a while
> on :( ) but it didn't compile because in the 2nd "when", I used
> mpl::vector<A> instead of vector1<A> and I didn't manage to figure out
> what the compile error meant. I tried the vararg and my other solution
> out of despair.This is a gotcha, no doubt. Sorry you got bit. Happens also with fusion::vector, so beware of templates with high arities. > Actually it is only almost the same solution, I actually had both > "when" in different order but I suppose in this case it doesn't > matter, right? No, in this case it doesn't matter. >> Incidentally, for the "state" parameter to fold_tree, you're using >> mpl::vector<>(). That works by luck. Because of the template arity >> thing, proto can't pull vector<> apart to check for nested transforms >> (but there are none anyway). You'll better express your intent with >> mpl::vector0<>(). > > Now I know it ;-) > I think this would be a good point for a "tips and tricks section". I > bet I won't be the last bitten by this one. Good suggestion. > Thanks a lot! No prob. -- Eric Niebler BoostPro Computing http://www.boostpro.com
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