On 02/24/14 05:04, Krzysztof Czainski wrote:

2014-02-24 11:55 GMT+01:00 MM <finjulhich@gmail.com <mailto:finjulhich@gmail.com>>:

Hello,

I just wanted to confirm there's no provided method to get the n'th element of say a fusion vector where n is known at runtime, except of handling it explicitkly with a switch case?

Thanks

MM

If such a function existed, what return type would it have?

Regards, Kris

What about: variant<T1,T2,T3> get(unsigned n, vector<T1,T2,T3>) ? For example: vector<T1,T2,T3> vec(T1(),T2(),T3()); variant<T1,T2,T3> var; var = get(2,vec); assert(var.which(),2); -regards, Larry

On 02/24/14 11:55, MM wrote:

On 24 February 2014 14:28, Larry Evans <cppljevans@suddenlink.net <mailto:cppljevans@suddenlink.net>> wrote:

On 02/24/14 05:04, Krzysztof Czainski wrote:

2014-02-24 11:55 GMT+01:00 MM <finjulhich@gmail.com <mailto:finjulhich@gmail.com> <mailto:finjulhich@gmail.com <mailto:finjulhich@gmail.com>>>__:

Hello,

I just wanted to confirm there's no provided method to get the n'th element of say a fusion vector where n is known at runtime, except of handling it explicitkly with a switch case?

Thanks

MM

If such a function existed, what return type would it have?

Regards, Kris

What about: variant<T1,T2,T3> get(unsigned n, vector<T1,T2,T3>) ? For example:

vector<T1,T2,T3> vec(T1(),T2(),T3()); variant<T1,T2,T3> var; var = get(2,vec); assert(var.which(),2);

-regards, Larry

Possible, a variant over the unique types in the sequence. What would the impl look like though?

I'd guess it would have switch statements, as you surmised in your OP. I'd also guess it could be implemented with some sort of vector of n functors, where n is the size of the fusion vector, and the i-th functor simply call fusion's get<i>(vec) and assigns the result to the variant. This vector of functors would then be used in the implementation of the get(i,vec) mentioned in my post. HTH -regards, Larry

On 02/24/14 11:55, MM wrote:

On 24 February 2014 14:28, Larry Evans <cppljevans@suddenlink.net <mailto:cppljevans@suddenlink.net>> wrote:

On 02/24/14 05:04, Krzysztof Czainski wrote:

2014-02-24 11:55 GMT+01:00 MM <finjulhich@gmail.com <mailto:finjulhich@gmail.com> <mailto:finjulhich@gmail.com <mailto:finjulhich@gmail.com>>>__:

Hello,

I just wanted to confirm there's no provided method to get the n'th element of say a fusion vector where n is known at runtime, except of handling it explicitkly with a switch case?

Thanks

MM

If such a function existed, what return type would it have?

Regards, Kris

What about: variant<T1,T2,T3> get(unsigned n, vector<T1,T2,T3>) ? For example:

vector<T1,T2,T3> vec(T1(),T2(),T3()); variant<T1,T2,T3> var; var = get(2,vec); assert(var.which(),2);

-regards, Larry

Possible, a variant over the unique types in the sequence.

It has to be over unique types because boost::variant cannot handle duplicates. However, if, instead of boost::variant, a truly tagged union: http://en.wikipedia.org/wiki/Tagged_union were used, then the types could be duplicated and there would be any need to program some metafunction to find the unique types in the fusion::vector<T1,T2,...,Tn>. Tagged unions were also requested here: http://stackoverflow.com/questions/17727563/tagged-unions-aka-variant-in-c-w... which also provided a link to an implementation of a tagged union.

What would the impl look like though?

MM

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On 25 February 2014 18:39, Matt Calabrese <rivorus@gmail.com> wrote:

Steven Watanabe proposed Boost.Switch years ago and I believe it was accepted but never added. It would work fine here to do what you want and has more general use than just fusion (and gives more information than a variant result would). I bring this up every time a question like this comes up but it would be nice for his library to be revived and added. :(

I found the header file here, I suppose that's all that's needed. http://dancinghacker.com/switch/switch.hpp MM