I would say trust but verify – there's always a chance that inference doesn't for some reason eliminate the branches. If that's the case, please file an issue (it will probably be fixed on master as soon as you hit the "New Issue" button; unless, of course, Jeff happens to be sleeping).
On Tue, Aug 26, 2014 at 4:49 PM, Michael Grant <[email protected]> wrote: > Thanks to both of you (and if others still wish to share experiences, > please, don't hestiate). Your "guiding principle" does indeed simplify my > thought process here. Indeed, the reason I asked in the first place is that > I have some code where conciseness demands the use of if statements; to > parametrize would require an undue amount of duplicated code. It's good to > know I can trust that the unused branches will be eliminated at compile > time. > > On Tuesday, August 26, 2014 3:41:13 PM UTC-5, Iain Dunning wrote: >> >> My guiding principle of Julia type stuff is the following: a version of a >> function is compiled for every type combination it is called with. Knowing >> that, all types become "crystallized" and propagate through, eliminating >> ifs and simplifying things. >> However, its been my experience with compilers in many langauges that >> there are often limits to how much is decided at compile time, normally due >> to a heuristic tradeoff between compilation time and run time of the >> function. >> >> For that reason, I try and use dispatch as I think it is cleaner than the >> ifs, even if they go away in the end. But I think people are needlessly >> afraid of using eltype because it seems like it'd be a run time check >> (Python people would definitely assume this). >> >> Best example I know is: >> https://github.com/IainNZ/GraphLayout.jl/blob/master/src/spring.jl#L42 >> >> if adj_matrix[i,j] != zero(eltype(adj_matrix)) || adj_matrix[j,i] != >> zero(eltype(adj_matrix)) >> >> which compiles down to >> >> if adj_matrix[i,j] != 0.0 || adj_matrix[j,i] != 0.0 >> >> or >> >> if adj_matrix[i,j] != false || adj_matrix[j,i] != false >> >> etc. I don't think people are used to this. >> >> Anyway, thats my 1c. >> >> On Tuesday, August 26, 2014 4:32:15 PM UTC-4, Stefan Karpinski wrote: >> >> It's kind of a toss up. These days, as you've noticed, they tend to >> produce identical results, which is nice. Once upon a time, the type >> parameter versions tended to produce better code, but that's not the case >> mostly anymore. So whichever is easier and clearer, I guess? If you need >> the type parameter for dispatch, then I guess I'd favor using it. >> >>
