[PyROOT] Segfault when creating proxy to derived class with multiple overloads

[stwunsch]

Following reproducer fails with a segfault:

import cppyy

cppyy.cppdef('''
struct Base {
    float data;
    float& operator[](int idx) { return data; }
};

struct Derived: public Base {
    float data;

    // Note that you have to derive from Base to make it break!
    float& operator[](int idx) { return data; }

    // Note that you must put the template here!
    template <typename T>
    float& operator[](int idx) { return data; }
};
''')

cppyy.gbl.Derived()

There's a corresponding issue submitted to upstream cppyy: https://bitbucket.org/wlav/cppyy/issues/334/segfault-when-creating-proxy-to-derived

This issues were found in the wake of RVec 2.0 (#7502) and may just scratch the surface of an issue in cppyy with picking up methods from derived classes. See the workarounds for operator[] and size in RVec 2.0 to avoid this problem.

[stwunsch]

Another reproducer pointing in the same direction is here. The iteration over the vector class fails because the size method is not picked up from the base class:

import ROOT

ROOT.gInterpreter.Declare('''
struct Base {
    std::vector<float> data;
    int size() { return data.size(); }
};

struct Vec : public Base {
    // using Base::size; // comment in this line to fix the iteration!
    void push_back(float x) { data.push_back(x); }
    float* begin() { return &data[0]; }
    float* end() { return &data[data.size() - 1]; }
    float& operator[](int idx) { return data[idx]; }
    void print() { for (auto x : data) std::cout << x << std::endl; }
};
''')

v = ROOT.Vec()
for i in [42, 43, 44]:
    v.push_back(i)
v.print()

c = 0
for x in v:
    print(c, x)
    if c > 10:
        raise Exception('Iteration failed!')
    c += 1

[dpiparo]

To be checked with the latest cppyy in the first place. Perhaps this will be fixed once we upgrade.

[guitargeek]

Indeed, this will be fixed with the CPyCppyy update.

[github-actions]

Hi @guitargeek,

It appears this issue is closed, but wasn't yet added to a project. Please add upcoming versions that will include the fix, or 'not applicable' otherwise.

Sincerely,
🤖