Re: [boost] Interest in a container which can hold multiple data types?

On 04 May 2015, at 18:51, Boris Rasin wrote:

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On 5/4/2015 6:33 PM, James Armstrong wrote: The main difference between this and a container of boost:any is that the container of boost::any still is a container of one data type, just being that one data type is a very flexible one. This container natively supports insertion of different data types. So, you could do,

int my_int = 5; double my_double0 = 9342.132; double my_double1 = 987.654; std::string my_string("This is a string."); std::vector<double> my_vec; my_vector.push_back(123.456);

omni my_container;

my_container.push_back(my_int); my_container.push_back(my_double); my_container.push_back(my_string); my_container.push_back(my_vector);

and the container happily stores the data.

This also works with std::vectorboost::any.

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You can then access the data through iterators

//access all doubles for (auto itr = my_container.begin<double>(); itr != my_containert.end<double>(); ++itr) { std::cout << *itr << std::endl; }

or through specifying the data type and index

//get the 0th element string std::cout << my_container.at<string>(0) << std::endl;

This could be useful, but wouldn't it be better to write this as generic algorithms capable of working with any container of boost::any, not just vector? Better yet, any container of type erased objects (boost::any, boost::variant, etc.) using something like boost::get<T>()?

I would actually prefer not to use type erasure: make a strong-typed and efficient heterogenous container. Something like this... ? template struct tuple_vector : std::tuple< std::vector<Args>... > { typename std::tuple type; template <typename T> void push_back(const T& value) { std::get< std::vector<T> >(*this).push_back(value); } template <typename T> void push_back( T&& value) { std::get< std::vector<T> >(*this).push_back(value); } }; struct Point { double x; double y; }; struct Line { double x; double y; double a; double l; }; struct Rectangle { double x; double y; double a; double w; double h; }; struct Circle { double x; double y; double r; }; tuple_vector shapes; shapes.push_back(Point{1.0, 1.0} ); shapes.push_back(Point{1.0, 1.0} ); shapes.push_back(Circle{1.0, 1.0, .3} ); shapes.push_back(Rectangle{0.0, 0.0, 0.0, 1.0, 1.0} );