library global variables

[nolta]

I'd like to add a function to access library global variables, e.g.,

x = cglobal(dlsym(lib,:var), Int32)

The following seems to work,

cglobal(p::Ptr, T::Type) = pointer_to_array(convert(Ptr{T}, p), (1,))[1]

but i'm opening this issue because there's probably a better way to do this.

[JeffBezanson]

Clever. While this may seem like a hack at first, maybe it's totally fine --- the interface to C variables can be creating a 1-element array that you read and write. I think cglobal should return that array, so it can be reused for each access.

[StefanKarpinski]

Yeah, that is very clever. Seems like a reasonable way to do this to me. The only issue is the interface to it — manipulating C globals via indexing with 1 seems pretty annoying.

[nolta]

Some interface options:

g = cglobal(ptr, typ)
x = g[1]
g[1] = y

g = cglobal(ptr, typ)
x = deref(g)
assign(g, y)

x = cglobal(ptr, typ)
cglobal(ptr, typ, y)

[StefanKarpinski]

Could also use a zero-dimensional array:

julia> g = Array(Int)
0-dimensional Int64 Array:
-4

julia> g[] = 1
1

Has the benefit that 0-d arrays always have a single unique value and can't be grown. Writing g[] and g[] = 2 doesn't seem terrible although it's not quite beautiful either.

[nolta]

Superseded by #1270.