Q: SWIG and dynamic attributes

[Anton D Kachalov]

Hello, all!

I have a question.
I develop a small library that has structure represented a few types in
union such as:

struct my_type {
   enum types;
   union {
      int i;
      float f;
      char *s;
   } u;
}

Some functions just return or pass-in "struct my_type". I would like to
make a bindings to Python/Ruby (and probably Perl) for that functions.
Moreover, I would like to convert "struct my_type" to native types of
destination scripting languages, e.g. lists/arrays, integers, strings
via %typemap(out) struct my_type or convert back from different types by
defining a number of same functions with different input variable types:

int my_func(int i) {
    struct my_type t; t.type = my_type_integer;
    t.u.i = i;
}

int my_func(float f) {
    struct my_type t; t.type = my_type_float;
    t.u.f = f;
}

int my_func(const char *s) {
    struct my_type t; t.type = my_type_string;
    t.u.s = strdup(s);
}
Is there a shorter way for input? Or just define function for each input
param type? May I accept as input some kind of "abstract" type of target
language and then convert content to my internal representation
utilizing "struct my_type"?

More over, my library has abstract "objects" that may have a number of
"attributes" that is defined and stored as a hash vector (pairs of
string and "struct my_type" values).
So, I would like to have ability to access those attributes from
Python/Ruby:
myobj = Mymodule::Object.new("I'm a string")
myobj.attrib1 = 0xdead
myobj.attrib2 = "foobar"
so, actually, Object class / structure doesn't have "attrib1/attrib2"
fields defined. They should be dynamically allocated. I know, that in
Python there is a __{set,get}attr__ methods that can be defined in the C
extension.
http://code.activestate.com/recipes/54352/ (this is a little bit
outdated example in the comment).

Is it possible to define something similar to __setattr__/__getattr__ in
SWIG for Python/Ruby bindings? Or redefine "." access methods in Ruby?
Or make some other hacks if itsn't possible to do within SWIG.

Thank you.

Rgds,
Anton

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[wsfulton]

Anton D Kachalov wrote:

> Hello, all!
>
> I have a question.
> I develop a small library that has structure represented a few types in
> union such as:
>
> struct my_type {
>    enum types;
>    union {
>       int i;
>       float f;
>       char *s;
>    } u;
> }
>
> Some functions just return or pass-in "struct my_type". I would like to
> make a bindings to Python/Ruby (and probably Perl) for that functions.
> Moreover, I would like to convert "struct my_type" to native types of
> destination scripting languages, e.g. lists/arrays, integers, strings
> via %typemap(out) struct my_type or convert back from different types by
> defining a number of same functions with different input variable types:
>
> int my_func(int i) {
>     struct my_type t; t.type = my_type_integer;
>     t.u.i = i;
> }
>
> int my_func(float f) {
>     struct my_type t; t.type = my_type_float;
>     t.u.f = f;
> }
>
> int my_func(const char *s) {
>     struct my_type t; t.type = my_type_string;
>     t.u.s = strdup(s);
> }
> Is there a shorter way for input? Or just define function for each input
> param type?

SWIG will only wrap what you give it, so you need to provide these
functions. You can make your code a bit shorter by using the
preprocessor and a C macro as SWIG has a preprocessor.

> May I accept as input some kind of "abstract" type of target
> language and then convert content to my internal representation
> utilizing "struct my_type"?
If you can write python/ruby/perl/whatever code in C to take your
abstract type and convert it to what is required to create a my_type,
then yes. You'd need to write typemaps for struct my_type to handle this.

William

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