Sorry, In Matlab there are these two functions that allow us to store any kind of matlab data (a struct, a cell array, a matrix) in a container of a handle to a GUI object (a button, an image, a figure ...) and later retrieve it with with
getappdata(handles, "container_name") I did the same with the IUP.jl <https://github.com/joa-quim/IUP.jl> (that you kindly visited before) C libraries. Here it's the C side that either gives me back the pointer to the stored data (previously stored with IUP istself) or the NULL pointer if the container is empty. I need to transfer that info back to Julia, which I do as function getappdata(hand::Ptr{Ihandle}, name::String) # Do the oposite of setappdata att = IupGetAttribute(hand, name) if (att != C_NULL) val = unsafe_pointer_to_objref(att) else val = [] end return val end So on the Julia side I need to be able to test if val is empty or not. The type of data store in 'val' is the users responsibility to know. Like in Matlab segunda-feira, 19 de Janeiro de 2015 às 18:08:34 UTC, Milan Bouchet-Valat escreveu: > > Le lundi 19 janvier 2015 à 09:48 -0800, J Luis a écrit : > > > > In Matlab, all variables are arrays, so testing for emptiness > > is (nearly) always possible, although not always meaningful. > > For example, what does isempty mean when applied to a file or > > a window? In matlab these are simply hardcoded to be false > > (not empty). > > > > What are you trying to do? > > > > I implemented a kind of setappdata/getappdata in IUP so I need to be > > able to test that the container is empty or not. But I don't know in > > advance what kind of data was stored in the container. > I'm not sure I get your idea. If you know that there's a container (say, > an Array), then you can just call length() and check that it's not 0, > disregarding the type of the container's elements. > > If the problem is that the user is allowed to pass a scalar instead of > an array, the solution is probably to forbid this, and require passing a > one-element array. This makes the code simpler and cleaner. > > Also, "setappdata/getappdata in IUP" does not evoke much to me. Care to > give more details? > > > Regards > > > > On Mon, Jan 19, 2015 at 8:42 AM J Luis <jmf...@gmail.com> > > wrote: > > Thanks but again no, they all suffer from the same > > illness > > > > julia> length(tp) > > ERROR: MethodError: `length` has no method matching > > length(::foo) > > > > segunda-feira, 19 de Janeiro de 2015 às 13:28:39 UTC, > > Kaj Wiik escreveu: > > What about simply length()? > > > > > > julia> a=[] > > 0-element Array{None,1} > > > > > > julia> length(a) > > 0 > > > > > > julia> a=[1,3] > > 2-element Array{Int64,1}: > > 1 > > 3 > > > > > > julia> length(a) > > 2 > > > > > > > > Kaj > > > > > > > > > >
