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Re: [rice] from_ruby on complex types (and to_ruby)

From:

Jason Roelofs

Date:

2010-05-28 @ 18:39

Derp, I was wrong about being wrong.... The to_ruby and from_ruby methods 
are *not* a member of the Rice namespace. Must be Friday...

To answer your question, I would recommend turning it into an Array and 
going from there:

Rice::Array arr(x.call("to_a"));

I have in the plans to build a proper way to let Rice deal with the 
nastiness of defining conversions from Ruby types to STL containers, but 
it's not going to be ready for a while, so this is the best answer I have 
for you, especially given Set is implemented in pure Ruby.

Jason

On May 28, 2010, at 2:26 PM, John O. Woods wrote:

> I was able to get it, finally, with one caveat.
> 
> For this code:
> 
> // Convert from Rice::Array to std::set
> template <>
> std::set<uint> from_ruby<std::set<uint> >(Rice::Object x) {
>     Rice::Array ary(x);
>     std::set<uint> result;
>     for (Rice::Array::iterator i = ary.begin(); i != ary.end(); ++i)
>         result.insert(Rice::from_ruby<uint>(*i)); // THIS LINE
>     return result;
> }
> 
> I get an error:
> 
> In file included from ../../../../ext/phenomatrix/id_dist.cpp:38:
> ../../../../ext/phenomatrix/ruby_conversions.h: In function ‘typename 
Rice::detail::from_ruby_<T>::Retval_T from_ruby(Rice::Object) [with T = 
std::set<unsigned int, std::less<unsigned int>, std::allocator<unsigned 
int> >]’:
> ../../../../ext/phenomatrix/ruby_conversions.h:23: error: ‘from_ruby’ is
not a member of ‘Rice’
> ../../../../ext/phenomatrix/ruby_conversions.h:23: error: expected 
primary-expression before ‘>’ token
> 
> It works fine if I remove the Rice::, for whatever reason. (I'm also 
using namespace rice now).
> 
> While I've got you on the line, here's a related question -- what if I 
were dealing with a Ruby set instead of a Ruby array? There's obviously a 
Rice::Array type, but how would one go about dealing with set? I suppose 
you could call to_a on the object, but I'm guessing there'd be a more 
efficient way to convert from Ruby set to std::set than through 
Rice::Array.
> 
> This is a purely hypothetical question. Please don't trouble yourself 
with it -- I was just wondering if you have an example handy, or could 
point me toward some resource.
> 
> John
> 
> On Fri, May 28, 2010 at 11:52 AM, Jason Roelofs <jameskilton@gmail.com> wrote:
> I'm guessing C++ simply isn't finding your from_ruby definition, you 
need to specify the template explicitly (return types don't work like 
parameters do):
> 
> std::set<uint> from_ruby< std::set<uint> >(Rice::Object x)
> 
> Also, I did forget to mention that the true prototype of these functions
are actually:
> 
> Rice::Object Rice::to_ruby<Type>(Type const & x)
> 
> Type Rice::from_ruby<Type>(Rice::Object x)
> 
> which is why your "using namespace Rice" makes a difference. Sorry about that.
> 
> As for donations, I appreciate the offer but don't have plans on opening
up donations to the project at this time. 
> 
> Jason
> 
> On May 28, 2010, at 12:29 PM, John O . Woods wrote:
> 
>> That example definitely works, but I'm having more trouble with std::set<uint>.
>> 
>> For example, I have a member function:
>> 
>> void push_mask(const set<uint>& mask_rows);
>> 
>> It's exposed to Ruby with:
>>  .define_method("push_mask", &PhenomatrixPair::push_mask)
>> 
>> And I have a from_ruby written:
>> 
>> // Convert from Rice::Array to std::set
>> std::set<uint> from_ruby(Rice::Object x) {
>>     Rice::Array ary(x);
>>     std::set<uint> result;
>>     for (Rice::Array::iterator i = ary.begin(); i != ary.end(); ++i)
>>         result.insert(from_ruby<uint>(*i));
>>     return result;
>> }
>> 
>> Compilation works fine, but when I try to run the tests, I get an error:
>> 
>>   1) Error:
>> test_push_and_pop_mask(TestPhenomatrixExtn):
>> ArgumentError: Unable to convert Array to std::set<unsigned int, 
std::less<unsigned int>, std::allocator<unsigned int> >*
>>     ./test/test_phenomatrix_pair_extn.rb:26:in `push_mask'
>>     ./test/test_phenomatrix_pair_extn.rb:26:in `test_push_and_pop_mask'
>> 
>> I've seen an error like this before when I forgot to put a using 
namespace rice; in my cpp file -- since it's a C extern. Is that the 
problem?
>> 
>> Incidentally, do you all have a donations page?
>> 
>> Thanks again,
>> John
>> 
>> 
>> 
>> 
>> On Fri, May 28, 2010 at 7:03 AM, Jason Roelofs <jameskilton@gmail.com> wrote:
>> First, you're right I definitely need to get some better documentation 
on to_/from_ruby, it can be a hard construct to understand at first.
>> 
>> As for your case, you've pretty much got what you would need to put in 
a to_ruby or from_ruby construct for your wrapper to work.
>> 
>> Given your to_h method, your to_ruby would simply look like (off the 
top of my head):
>> 
>> Rice::Object to_ruby(cparams const & param) {
>>  return param.to_h();
>> }
>> 
>> And then you can use Rice::Hash to make your from_ruby a bit cleaner:
>> 
>> cparams from_ruby<cparams>(Rice::Object x) {
>>  Rice::Hash hash(x);
>>  cparams params( hash[ Rice::Symbol("classifier") ].str() );
>>  params.k = from_ruby<uint>(hash[Rice::Symbol("k")]);
>> 
>>  return params;
>> }
>> 
>> Let me know if this works / doesn't work.
>> 
>> Jason
>> 
>> 
>> On May 27, 2010, at 3:07 PM, John O. Woods wrote:
>> 
>> > I'm not quite clear how to implement from_ruby for different complex 
types in C++.
>> >
>> > For example, right now, I have this object that should be really easy
to turn into an :options => {:symbol => true, :other_symbol => false} type
of hash (as used in Rails).
>> >
>> > using std::string;
>> > class cparams {
>> > public:
>> >     cparams(const string& name) : classifier(name), k(0) { }
>> >
>> >     string classifier;
>> >     uint k;
>> >
>> > #ifdef RICE
>> >     Rice::Object to_h() const {
>> >         Rice::Hash h;
>> >         h[ Rice::Symbol("classifier")   ]   = to_ruby<string>(classifier);
>> >         if (k > 0) h[ Rice::Symbol("k") ]   = to_ruby<uint>(k);
>> >         return h;
>> >     }
>> > #endif
>> > };
>> >
>> > I can use to_h() to easily convert to a Ruby type, but my 
understanding is there's a way to do it automatically.
>> >
>> > Additionally, I have this little gem elsewhere in my code:
>> > DistanceMatrix::DistanceMatrix(const Array& source_matrix_ids, 
Rice::Object classifier_params_h)
>> >     // Convert from Hash to cparams
>> >     cparams classifier_params( 
from_ruby<Rice::Symbol>(classifier_params_h.call("fetch", 
Rice::Symbol("classifier"))).str() );
>> >     classifier_params.k = 
from_ruby<uint>(classifier_params_h.call("fetch", Rice::Symbol("k")));
>> >     // ...
>> >
>> > Ack! How would I write a from_ruby handler for something like this? 
Perhaps you've got an example somewhere that I just haven't been able to 
find?
>> >
>> > Perhaps you could add it to the FAQ? I see the theoretical 
explanation of from_ruby and to_ruby, but I don't know enough about the C 
side of Ruby -- or Rice for that matter -- to grok it.
>> >
>> > Many thanks,
>> > John
>> 
>> 
> 
>