On Tuesday, May 24, 2016 at 3:01:12 PM UTC-4, Gabriel Gellner wrote: > > Working thru the incredible guide: > http://julialang.org/blog/2013/05/callback > > I am stuck on understanding if there are any work arounds for being able > to use julia anonymous functions in `ccall` callback functions. > Specifically I am interested in the common case of wanting to use function > parameters without having to do the C convention of passing around a void > *param pointer as the last argument of the callback. > (ie instead of having func(x, y, param) I could do (x, y) -> func(x, y, a, > b) to set the values for the parameters of a julia callback function that > is passed to a ccall routine) >
As explained in the guide (see the qsort_r example), you only need for the C API to have a void* pointer that you pass around. On the Julia side, this can be completely hidden from the caller. (e.g. in the qsort_r example, the Julia lessthan function passed to qsort! does not need a "param" argument.) (This is how NLopt.jl, Cubature.jl, etcetera work: the C API uses void* pointers, but this is hidden from the Julia callers exactly as described in the blog post.)
