Thanks again for your help. I was also able to get that example to compile, which was perfect. Unfortunately, it seems rather fragile. I had copied most of the pieces over into a split test.hpp/test.cpp, and kept getting errors. I did eventually resolve the problem by more completely replacing them with your code directly, but I wasn't able to figure out what was causing the problem. Of course, that means when I tried to apply it to my real code, I ended up with the same error:

solution.hpp:36:3: error: template argument 1 is invalid
solution.hpp:36:4: error: expected identifier before ‘::’ token
solution.hpp:36:6: error: typedef name may not be a nested-name-specifier
solution.hpp:36:6: error: expected ‘;’ at end of member declaration
solution.hpp:36:11: error: ‘type’ does not name a type
solution.hpp:52:3: error: template argument 1 is invalid
solution.hpp:52:4: error: expected identifier before ‘::’ token
solution.hpp:52:6: error: typedef name may not be a nested-name-specifier
solution.hpp:52:6: error: expected ‘;’ at end of member declaration
solution.hpp:52:11: error: ‘type’ does not name a type

the relevant pieces of code were the following:

31 template<class T>
32 struct get_neighborhood_type {
33   typedef typename mpl::eval_if<is_placeholder<T>,
34     mpl::identity<void>,
35     get_neighborhood_type_impl<T>
36   >::type type;
37 };


47 template<class T>
48 struct get_iterator_type {
49   typedef typename mpl::eval_if<is_placeholder<T>,
50     mpl::identity<void>,
51     get_iterator_type_impl<T>
52   >::type type;
53 };

which are pretty much the same as what you sent me, but with the names changed. Are there any likely causes of these errors that occur to you, so I can try so fix them in a somewhat intelligent fashion?



On Tue, Mar 11, 2014 at 6:57 PM, Steven Watanabe <> wrote:

On 03/11/2014 01:42 PM, Samuel Christie wrote:
> I'm not sure how to do the get_collection_type deduction in such a way that
> it works for more than one type of collection. I.e., both a vector<T> and a
> Collection as defined above.

You can either use a nested typedef (like T::iterator)
or you can use decltype(boost::declval<T>().collection()).

> I also tried to do a test with the slightly more basic vector<Test>
> collection type. I got close, but I eventually had issues with the !=
> required by the foreach loop pattern.

That shouldn't have been a problem, since
equality_comparable defines both == and !=.

> Here's a paste of most of the test code:
> Hopefully what I'm having trouble with makes sense to you; if not, maybe
> just providing a few more examples of the pieces required to make a
> for(auto i : t.collection()) work based on the above class declaration
> would be helpful. I feel like either I'm getting close, or I'm trying to do
> something I shouldn't be.

You're really close.  I've gotten your example
working.  See attached.  (I also cleaned it up
Tested with MSVC 12 and GCC 4.7.

In Christ,
Steven Watanabe

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