Re: [Boost-users] Map runtime value to type

Leon Mlakar writes:

...

Say I have this code. struct A {}; struct B {}; enum useType {useA, useB};

template <typename F> void g(useType w, F f) { switch (w) { case useA: A a; f(a); case useB: B b; f(b); } }

I need to generalize this to any number of enum values and any number

of

...

corresponding types.

Something like this (pseudocode):

typedef compile_time_map< mpl::pair, mpl::pair, ... > mapping;

template <typename F> void g(useType w, F f) { switch_apply( w, mapping, f ); }

Why not:

std::map> use_map = { { useA, [] { A a; f(a); } }, { useB, [] { B b, f(b); } } };

Thanks for all the ideas. I found a solution [1] based on boost::fusion::for_each() which looks good enough for me (no variant, no heap allocations, no type-erasure). I believe it should be functionally equivalent to an if-else chain, and not as efficient as an actual switch, though. Regards [1] http://stackoverflow.com/questions/26846299/boost-fusion-run-time- switch