Re: [Boost-users] [fusion][?] a dictionary with compile time (or types as) keys

On Feb 17, 2014, at 8:20 AM, Larry Evans wrote:

...

On 02/16/14 12:30, Nick Stokes wrote: The problem is the following:

class TypeDictionary { public: // implementation be here -- and the question is about this };

struct Foo; struct Bar;

void userOfTypeDictionary() {

TypeDictionary td; td.insert( Foo() ); td.insert( Bar() ); td,insert( double(3.14) ); // and other unknown (to TypeDictionary) // list of types attached

// later on, in a different scope perhaps Foo& f = td.get<Foo>() ; Bar& f = td.get<Bar>(); double pi = tg.get<double>(); // ... }

Now the question so far seems like right up in the alley of Boost.Fusion, perhaps with a boost::fusion::set, but I am unsure how to manipulate a set of types unknown ahead of time as in code above, and with a -- rather obvious -- extension whereby different instances of TypeDictionary would be used to contain a different set of types, potentially in different compilation units.

As for a realistic motivating use case, think of a plugin manager. At any given time of its life an arbitrary heterogeneous set of objects are attached to it, and the it is the manager's job to manage the life time of the attached objects and return (a reference) to them when queried in a type-safe manner.

Any ideas on whether such a thing is possible, and how, would be deeply appreciated.

Thanks many, Nick Wouldn't:

http://www.boost.org/doc/libs/1_55_0/libs/fusion/doc/html/fusion/container/m...

work?

I think the OP is looking for something runtime, i.e. type-erased. I know I have seen such a thing but I don't recall seeing one in Boost. Cheers, Gordon