std::vector to java.util.Vector code generation with swig

c++, java, list, swig, vector

Solution

You don't really want to be touching `java.util.Vector` with your wrapped interfaces because you will end up duplicating storage or making large numbers of copy operations every time you pass it in/out of a function. (Note also that in general in C++ inhering from containers is odd design).

Instead in Java the "right" thing to do is to inherit from `java.util.AbstractList`. This answer is a more generic version of my older answer to a similar question.

It works for all `std::vector` types, not just a fixed type and handles primitives which need to be accessed via Objects using an "autobox" custom type map. It's missing support for the specialized `std::vector<bool>`, but that should be simple to add if you need it.

%{
#include <vector>
#include <stdexcept>
%}

%include <stdint.i>
%include <std_except.i>

namespace std {

    template<class T> class vector {
      public:
        typedef size_t size_type;
        typedef T value_type;
        typedef const value_type& const_reference;
        vector();
        vector(size_type n);
        vector(const vector& o);
        size_type capacity() const;
        void reserve(size_type n);
        %rename(isEmpty) empty;
        bool empty() const;
        void clear();
        void push_back(const value_type& x);
        %extend {
            const_reference get(int i) const throw (std::out_of_range) {
                return $self->at(i);
            }
            value_type set(int i, const value_type& VECTOR_VALUE_IN) throw (std::out_of_range) {
                const T old = $self->at(i);
                $self->at(i) = VECTOR_VALUE_IN;
                return old;
            }
            int32_t size() const {
              return $self->size();
            }
            void removeRange(int32_t from, int32_t to) {
              $self->erase($self->begin()+from, $self->begin()+to);
            }
        }
    };
}

// Java typemaps for autoboxing in return types of generics
%define AUTOBOX(CTYPE, JTYPE)
%typemap(autobox) CTYPE, const CTYPE&, CTYPE& "JTYPE"
%enddef
AUTOBOX(double, Double)
AUTOBOX(float, Float)
AUTOBOX(boolean, Boolean)
AUTOBOX(signed char, Byte)
AUTOBOX(short, Short)
AUTOBOX(int, Integer)
AUTOBOX(long, Long)
AUTOBOX(SWIGTYPE, $typemap(jstype,$1_basetype))

%typemap(javabase) std::vector "java.util.AbstractList<$typemap(autobox,$1_basetype::value_type)>"
%typemap(javainterface) std::vector "java.util.RandomAccess"
%typemap(jstype) std::vector get "$typemap(autobox,$1_basetype)"
%typemap(jstype) std::vector set "$typemap(autobox,$1_basetype)"
%typemap(jstype) std::vector &VECTOR_VALUE_IN "$typemap(autobox,$1_basetype)"
%typemap(javacode) std::vector %{
  $javaclassname(java.util.Collection<$typemap(autobox,$1_basetype::value_type)> e) {
    this.reserve(e.size());
    for($typemap(autobox,$1_basetype::value_type) value: e) {
      this.push_back(value);
    }
  }
%}

Most of this is fairly similar to the default std_vector.i that SWIG currently provides, the new bits are the renaming, extending and typemaps that extend `AbstractList` and implement `RandomAccess`. It also adds a constructor that takes other `Collection`s - this is recommended by the Java documentation and easy enough to do. (There's an overload for other `std::vector` types which is much faster).

I tested this vector wrapping within another SWIG interface:

%module test

%include "vector.i"

%template(DblVec) std::vector<double>;
%template(ByteVec) std::vector<signed char>;
%include <std_string.i>
%template(StringVec) std::vector<std::string>;

%inline %{
struct foo {};
%}

%template(FooVec) std::vector<foo>;

Which I was able to compile and run with:

public class run {
  public static void main(String argv[]) {
    System.loadLibrary("test");
    DblVec dv = new DblVec(100);
    for (int i = 0; i < 100; ++i) {
      dv.set(i,(double)i);
    }
    FooVec fv = new FooVec(1);
    fv.set(0, new foo());
    for (double d: dv) {
      System.out.println(d);
    }
  }
}

Problem

I try to generate java code with SWIG In MyList.h I declared a custom list object called _list ``` List<T*> _list; ``` and this List class inherits from vector ``` class List : public vector<T> ``` In a business class (in C++) I return a List of custom objects ``` List<MyObject> getMyList(){ .... return list; } ``` so I want to generate java code where I can retrieve this C++ List as java.util.List or java.util.Vector. in my swig.i file I couldn't manage how to embody ``` %typemap(jstype) List "java.util.Vector" namespace std { %template(CustomVector) vector<MyObject>; } ``` any kind help how to configure this swig.i template file or some sample code to generate a java.util.List / Vector returning function will be appreciated. Thank you.

Original source

Related problems