Re: [igraph] Igraph with JNI

[Tamas Nepusz]

> The following data structure can't be mapped directly:
> igragh_vector_t
I guess these should be mapped to a Java double[], but since I have no  
experience with JNA, I don't know how to do that. If I'd have to do  
the same in JNI, I would possibly write a converter function in both  
directions. A more Java-ish way would possibly be to allow any Java  
Collection of doubles (i.e., ArrayLists, Vectors and so on) to be  
converted to igraph_vector_t. Note that you don't have to map the  
_internal_ elements of igraph_vector_t to Java types, I'd simply  
create an igraph_vector_t on the fly from an incoming double[] when  
needed and convert outgoing igraph_vector_t objects back to double[].  
The same for igraph_vector_bool_t and igraph_matrix_t (bool[] and  
double[][]).

By the way, when trying to map igraph_t to a Java object, I would  
simply create a proxy Graph class that holds the _memory address_ of  
the underlying igraph_t object (cast to a Java long), so I would't try  
mapping each member of the igraph_t struct to Java types. But that's  
just a matter of taste, the Python interface uses this approach, while  
the R interface doesn't (as far as I know).

> There are several work arounds:
> 1. To write a wrapper function to convert primitive java types into  
> igraph types. For example, when a java int[] array is passed,  
> convert to igraph_vector_t first, after computation, assign the  
> values back into int[] array, this will automatically pass the  
> values back to java as the java int[] array were passed into c by  
> reference.
I think that's the most reasonable approach for vector types. (Or, if  
there's a faster way to copy large chunks of data directly without  
using a for loop, like memcpy() in C).

> 3. Re-implement the data types in java. This also require me to know  
> the structure of these datatypes
I wouldn't do that as the internal structure of igraph types may  
change without further notice between releases, and then you would  
have to adapt your interface as well.

--
Tamas