How to wrap a class derived from vector in swig - c++

Question

I want to wrap a class derived from std::vector with some extend functions into csharp with swig. the functions from vector are also needed like push_back to add new item into the class (which named Add in csharp).
I tried with default setting with swig, IntArray is valid in csharp .But, vector's functions are invalid.
if i try to define a vector in the .i file:
namespace std{
%template(ScalarVec) vector<ScalarTest>;
}
a class named ScalarVec have functions like vector is valid in csharp, but without the extend function.
How to wrap the ScalarArray to csharp with swig?
The following is a simple example.
#include <vector>
#include <numeric>
namespace test
{
struct ScalarTest {
int val;
};
struct ScalarArray : public std::vector<ScalarTest>
{
int sum() const {
int res = 0;
for (const ScalarTest &item : *this) {
res += item.val;
}
return res;
}
};
}

Answer 1

SWIG is picky about order of declarations. Below correctly wraps your example code and can call the sum function. I'm not set up for C# so the demo is created for Python:
test.i
%module test
%{
// Code to wrap
#include <vector>
#include <numeric>
namespace test
{
struct ScalarTest {
int val;
};
struct ScalarArray : public std::vector<ScalarTest>
{
int sum() const {
int res = 0;
for (const ScalarTest &item : *this) {
res += item.val;
}
return res;
}
};
}
%}
namespace test
{
struct ScalarTest {
int val;
};
}
%include <std_vector.i>
// Must declare ScalarTest above before instantiating template here
%template(ScalarVec) std::vector<test::ScalarTest>;
// Now declare the interface for SWIG to wrap
namespace test
{
struct ScalarArray : public std::vector<ScalarTest>
{
int sum() const;
};
}
demo.py
import test
x = test.ScalarArray()
a = test.ScalarTest()
a.val = 1
b = test.ScalarTest()
b.val = 2
x.push_back(a)
x.push_back(b)
print('sum',x.sum())
print(x[0].val,x[1].val)
Output:
sum 3
1 2