> > Le 31 mars 2016 ? 13:32, Keith Medcalf <kmedcalf at dessus.com> a ?crit : > > > > On the third hand, this could be a case of premature optimization and > the optimal course of action is not to optimize the action before doing > it, but as Nike says, "Just Do It". > > I agree on the generic point, though here the desire to call another > existing function from the implementation of a new one is merely a 'code > reuse' point of view (not to re-invent/re-code things perfectly already > implemented). :)
You can call strftime just perfectly dandily and reuse that code, which exists in the platform runtime libraries. Now if you had to re-implement strftime, I could see your point. But you aren't. You are just setting up some parameters and calling it. > > Le 31 mars 2016 ? 14:09, Hick Gunter <hick at scigames.at> a ?crit : > > > > While it is technically possible to convincingly fake an SQLite context > to call strftimeFunc() with, it also means that you are ignoring SQLite > function overloading. And making yourself dependant on internal changes to > SQLite structures that are opaque for a reason. > > I never intended to hack the code, make strftimeFunc() non static to call > it from elsewhere (out of sqlite code). My question was: is there a > supported API function (a single one would be enough), to relay a call to > the internal implementation of some function. > > > Consider this theoretical case: in an application (not in a custom build > of sqlite itself) I'd want to implement a function "date(...)", > overloading/replacing the default date(). That is easy to do, and works > fine. Now suppose I only have to check for some parameters not handled by > the default date(), build a new set of parameters (standard looking after > whatever conversion / preparation I had to do), call the original date() > function (same context), get its result and forward it to my caller. > > I can't. I can't call the initial implementation (or even the previously > stacked one - if there was a stacking which I'm not sure). And I can't > really built a SQL statement and execute it: if I'm using date() function > in the SQL statement, chances are that statement will call *my* version > which is current and not the initial implementation. > > Note that I did simplify the problem I was trying to solve and reduced it > to calls of date() taking a single parameter. Simply registering a new > function date() taking a single parameter works fine. Calls with a single > parameter call my implementation and calls with none or 2 or more > parameters call the original default implementation. In this case, I have > the solution. The real problem at hand was simpler than the generalization > I posted about. > > There is no bug, or problem to solve in SQLite here. Just maybe a single > C-API function to consider for addition at some point in the future. > > Thanks you all, > -- > Meilleures salutations, Met vriendelijke groeten, Best Regards, > Olivier Mascia, integral.be/om > > > Context, initial post: > > > Le 30 mars 2016 ? 20:04, Olivier Mascia <om at integral.be> a ?crit : > > > > Hello, > > > > Writing a scalar SQL function, is there a C-level way to call some other > scalar SQL function? > > For instance, writing some specialized date_xyz(), could it be possible > to prepare some arguments and call strftime()? > > > > I see in the code that strftimeFunc() is the implementation for the > predefined strftime(), and I see no huge difficulty calling it from my own > function, but of course it is internal (static). Did I miss something in > the API that would let me get a hand on it? Something like some > 'sqlite3_call_function(...)' which would take the function name as text > and let me hand it the context, count of arguments, array of them, and > return me somehow a sqlite_value with the result? > > > > I think it is obvious I could build a SQL statement from within the > function and execute it. But it sounds costly to involve the parser (yes, > it's fast) for that, isn't it? > > > > -- > > Meilleures salutations, Met vriendelijke groeten, Best Regards, > > Olivier Mascia, integral.be/om > > > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
