On 26 March 2012 11:36, Stewart Gordon <smjg_1...@yahoo.com> wrote: > I'm coming up against some interesting challenges while porting stuff in my > utility library to D2. > > Firstly, D2 uses opBinary and opOpAssign, rather than the operator-specific > op* and op*Assign. While the latter still work, they aren't mentioned in > the current D2 docs. Which would imply that they're on the way out; however, > there's no mention at > https://github.com/D-Programming-Language/d-programming-language.org/blob/master/deprecate.dd > > (See also > http://d.puremagic.com/issues/show_bug.cgi?id=7779 ) > > Still, it seems clear that opBinary/opOpAssign is the D2 way of doing it. > But it has the drawback that, because it's a template, it isn't virtual. > One way about it is to keep the D1-style op functions and make > opUnary/opBinary/opOpAssign call these. But is there a better way? > > The other isn't a D2-specific issue, though D2 increases the significance of > it. I have a method with the signature > > Set opAnd(bool delegate(Element) dg) > > I would like to enable a user of the library to pass in a delegate whose > parameter is any type to which Element is implicitly convertible. This > could be the same type as Element with the top-level constancy changed > (probably the main use case), or a type that is distinct beyond the > constancy level. Turning it into a template > > Set opAnd(E)(bool delegate(E) dg) > > would address this, but prevent overriding with the appropriate code for > each set implementation. > > Who else has been faced with this problem? Have you found a good way of > dealing with it? > > Stewart.
Non-virtuality of templates is a general problem at the moment. The issues seem to be around how to handle inheritance of template arguments, and how to dispatch the functions based on a combination of template arguments and class hierarchy. This is a hard problem with no obvious answer. in terms of trying to work around it, perhaps compile-time reflection could help, I haven't encountered this before, but that's where I would start. -- James Miller
