there's a classic problem in computer science on extending apis with both functions and state, and i remember a julia talk or paper saying that multiple dispatch solved this nicely.
so i think reading that might help, but i can't remember what it's called (it the ... problem and i think there was a haskell paper by walder on it... andrew On Saturday, 28 December 2013 11:31:07 UTC-3, andrew cooke wrote: > > thanks. i've done almost exactly the same thing with the "Nothing" type > at > https://github.com/andrewcooke/BlockCipherSelfStudy.jl/blob/master/src/GA.jl > > i don't think my problem is specific to GA. the problem is how to add > extra state to an api. > > in traditional OO you can use inheritance to create a new class with the > extra state. > > in julia you cannot. nor can you add it inside closures because you can't > (as far as i can tell) extend methods in another module with a closure. > > so instead you have to spot ahead of time that a user might want to add > extra state and provide an additional parameterized field (the "context" in > my code linked to above) where the user can store arbitrary information. > > which seems ugly and prone to errors (what if you miss somewhere)? > > so i still hope there's a better solution. > > cheers, andrew > > On Saturday, 28 December 2013 04:50:11 UTC-3, Toivo Henningsson wrote: >> >> I don't have enough background in genetic algorithms to understand what >> you are trying to accomplish, but I think that to answer the question of >> how to write code so that it can be generally extended by users, the first >> thing to ask is what the interface to the code that you want to write >> really is (in abstract terms). Then, one can start to model it with types, >> generic functions, inheritance, etc. >> >> Also, to create a generic function without actually providing any >> implementations, I've lately been using things like >> >> f(::None) = nothing >> >> which seems to work fine. >> >> >>
