Fix struct reference in docs

[kmsquire]

As noted here, the docs still incorrectly state that

Currently, it is not possible to pass structs and other non-primitive types from Julia to C libraries.

at the end of the first section here.

[kmsquire]

Actually, in the same post on Google docs, Jameson also stated that

There is a section in the manual about how to pass struct a to/from C.

I was looking for that, but couldn't find it in the latest docs. Did I miss it?

[vtjnash]

hm, technically that statement isn't wrong – you can't pass structs and other non-primitive types from Julia to C (#3466), but it's misleading, since you can pass pointers to structs (pointers being a primitive types) and that's what you actually want to do about 99% of the time anyways.

http://docs.julialang.org/en/latest/manual/calling-c-and-fortran-code/#type-correspondences

[kmsquire]

Yep, that makes sense. Maybe it would be good to clarify that you can pass pointers to structs in that statement (which is what I'm doing, of course).

I did find that table after I wrote the second comment. I think I was looking for something more, but maybe I'll try to write something up myself at some point.

[binarybana]

+1 for more description regarding this. The first time I needed to pass a pointer to a Julia struct I felt like I was floating over uncharted waters because I didn't appreciate the primitive type/pointer distinction.

[ihnorton]

Can this be closed? There is some discussion about by-value vs pointer to structs at http://docs.julialang.org/en/latest/manual/calling-c-and-fortran-code/#mapping-c-types-to-julia (two paragraphs above that anchor)

[kmsquire]

No longer an issue, as the relevant text (and functionality) has totally changed.