right, you can't mutate it directly, but you can make a new copy with the intended changes, then use unsafe_store to write those changes back into the struct.
On Mon, Aug 10, 2015 at 3:56 PM J Luis <jmfl...@gmail.com> wrote: > ... amd I am using unsafe_load() > > > S0 = unsafe_load(unsafe_load(TTABLE.segment,1),1) # > ::GMT.GMT_TEXTSEGMENT > https://github.com/joa-quim/GMT.jl/blob/master/src/gmt_main.jl#L860 > > but if I add this line after > > S0.n_rows = 2 > > ERROR: type GMT_TEXTSEGMENT is immutable > in GMTJL_Text_init at C:\progs_cygw\GMTdev\GMT.jl\src\gmt_main.jl:861 > > > > segunda-feira, 10 de Agosto de 2015 às 20:47:27 UTC+1, J Luis escreveu: >> >> >> >> segunda-feira, 10 de Agosto de 2015 às 20:15:57 UTC+1, Jameson escreveu: >>> >>> My suggestion would be to mirror only the parts of those structs that >>> are part of the public API. Then use unsafe_load / unsafe_store to read / >>> modify / write the intended changes. The API authors were nice to put the >>> public fields at the top so that you can do this (many libraries don't / >>> can't do this). Then the "real" object will always be the Ptr to the one >>> allocated by GMT, and you only have temporary copies of them alive at any >>> time inside Julia. >>> >> >> But GMT_TEXTSEGMENT is part of the GMT API (hm, have to check why it >> doesn't show up in http://gmt.soest.hawaii.edu/doc/latest/GMT_API.html) >> >> Sorry, to be concrete, and repeating myself. I need to change n_rows of >> >> >> http://gmt.soest.hawaii.edu/projects/gmt/repository/entry/branches/5.2.0/src/gmt_resources.h#L517 >> >> Can I do it? >> >> BTW, I'm a developer of GMT (that's why I could create that backdoor >> function that temporarily saved me on this), although the API was all >> created by P. Wessel. >> >> >> >>> >>> >>> On Mon, Aug 10, 2015 at 2:53 PM J Luis <jmf...@gmail.com> wrote: >>> >>>> >>>> >>>>> usually, there's is one big toplevel distinction driven by who will >>>>> free the memory: if C will be freeing the memory, then you must always >>>>> have >>>>> the C code also allocating the memory (hopefully the library author >>>>> provide >>>>> some sort of new / alloc / create function, although sometimes they rely >>>>> on >>>>> the user calling malloc). >>>>> >>>> >>>> Yes, the GMT_Create_Data (that ccals a C function with the same name) >>>> does that. >>>> >>>> https://github.com/joa-quim/GMT.jl/blob/master/src/gmt_main.jl#L852 >>>> <https://github.com/joa-quim/GMT.jl/blob/master/src/gmt_main.jl#L852> >>>> >>>>> >>>>> > Is that really impossible and I'm doomed to the path exemplified >>>>> with that C GMT_blind_change_struct() function? >>>>> >>>>> ideally, C libraries that expect to manage a struct's memory also >>>>> provide accessor methods to read any of the structs important fields so >>>>> that you can always declare its type as Ptr{Void} in Julia. However, I >>>>> realize this is true of many C libraries. >>>>> >>>> >>>> >>>> The pointers are ok, my real problem are those 'scalars' like the >>>> n_rows in >>>> >>>> >>>> http://gmt.soest.hawaii.edu/projects/gmt/repository/entry/branches/5.2.0/src/gmt_resources.h#L517 >>>> >>>> I only know the number of rows after having read the data and than the >>>> immut is already created >>>> >>>> >>>>> >>>>> >>>>> On Mon, Aug 10, 2015 at 9:58 AM J Luis <jmf...@gmail.com> wrote: >>>>> >>>>>> >>>>>> >>>>>> segunda-feira, 10 de Agosto de 2015 às 14:15:15 UTC+1, Isaiah >>>>>> escreveu: >>>>>>> >>>>>>> https://github.com/JuliaLang/julia/pull/12113 >>>>>>> >>>>>> >>>>>> So there is hope. Thanks >>>>>> >>>>>> >>>>>> >>>>>>> >>>>>>> >>>>>>> On Mon, Aug 10, 2015 at 8:11 AM, J Luis <jmf...@gmail.com> wrote: >>>>>>> >>>>>>>> Hi, >>>>>>>> >>>>>>>> Let me try to explain my need to fight with immutables. I made >>>>>>>> another round to my GMT wrapper (which is hopefully almost ready) and >>>>>>>> struggled again with the immutables. The point is that GMT API structs >>>>>>>> are >>>>>>>> deeply nested and need to be mirrored with immutables (otherwise Julia >>>>>>>> crashes). Namely this one >>>>>>>> >>>>>>>> >>>>>>>> https://github.com/joa-quim/GMT.jl/blob/master/src/libgmt_h.jl#L1445 >>>>>>>> >>>>>>>> so I first went with the advised solution of creating and filling >>>>>>>> the type is julia and replace the pointees of the immutable type, >>>>>>>> which I >>>>>>>> did here (see the commented code): >>>>>>>> >>>>>>>> >>>>>>>> https://github.com/joa-quim/GMT.jl/blob/master/src/gmt_main.jl#L874 >>>>>>>> >>>>>>>> but the problem now is that *TS* is a memory owned by Julia and >>>>>>>> that will be fatal when GMT's own memory cleaning functions try to >>>>>>>> free it >>>>>>>> and -> Julia crashes. >>>>>>>> So if use a pure Julia solution I've no choice but to let memory >>>>>>>> leeks and other house keeping to be done. Not good at all. >>>>>>>> >>>>>>>> For the time being I ended up with this ugly C trick of sending to >>>>>>>> C the job of changing some members (non-pointers) that need absolutely >>>>>>>> to >>>>>>>> changed after the type has been created >>>>>>>> >>>>>>>> >>>>>>>> http://gmt.soest.hawaii.edu/projects/gmt/repository/entry/branches/5.2.0/src/gmt_api.c#L7376 >>>>>>>> >>>>>>>> but besides being ugly I've no guarantee that I can convince my >>>>>>>> partners to let that backdoor go into the GMT lib. I much lovelier >>>>>>>> trick >>>>>>>> would be if this chunk only of that backdoor function would work. >>>>>>>> >>>>>>>> else if (!strncmp (keyword, "API_POINTER_", 12U)) { /* >>>>>>>> Blindly change a pointer to a scalar. Irritatingly Julia ignores this >>>>>>>> */ >>>>>>>> if (!strcmp(&keyword[12], "UINT64")) >>>>>>>> *(uint64_t *)ptr = *(uint64_t *)what; >>>>>>>> } >>>>>>>> >>>>>>>> but the problem is that I am not able to get from Julia the >>>>>>>> pointers address that would make that work. I tried with >>>>>>>> >>>>>>>> pointer(S0.n_rows) >>>>>>>> >>>>>>>> and >>>>>>>> >>>>>>>> pointer_from_objref(S0.n_rows) >>>>>>>> >>>>>>>> and others, but nothing. It seams to work in the C side (I can see >>>>>>>> it with the debugger when I set in that piece of code) but than nothing >>>>>>>> changes. The C struct doesn't change. >>>>>>>> Is there a way to get the C pointer address from Julia? >>>>>>>> >>>>>>>> So, I guess my question is: >>>>>>>> >>>>>>>> How do we do to change immutable members that are not pointers? >>>>>>>> Is that really impossible and I'm doomed to the path >>>>>>>> exemplified with that C GMT_blind_change_struct() function? >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>
