Add unit test for function that takes multiple string views

[guitargeek]

Taken from wlav/CPyCppyy#13

[wlav]

The test needs a doc string (see other examples) as that will be printed when running pytest -v.

[guitargeek]

Ok! I'm still trying to understand why the tests fails with CPyCppyy master.

If I remove this newly added code here, it works:
https://github.com/wlav/CPyCppyy/blob/master/src/Converters.cxx#L1950

// for Python str object: convert to single char string in buffer and take a view
    if (CPyCppyy_PyUnicodeAsBytes2Buffer(pyobject, fStringBuffer)) {
        fStringViewBuffer = fStringBuffer;
        para.fValue.fVoidp = &fStringViewBuffer;
        para.fTypeCode = 'V';
        return true;
    }

But I can't see anything wrong with it!

HasState() of the STLStringViewConverter is correctly overridden...

[guitargeek]

Hi @wlav, I understand now better what is going on, see this simpler reproducer:

import cppyy

s1 = cppyy.gbl.std.string(b"s1")
s2 = cppyy.gbl.std.string(b"s2")

v1 = cppyy.gbl.std.string_view(s1)
print(v1)

cppyy.gbl.std.string_view(s2)
print(v1)

s1
s2

The problem is not the string converter in particular, but the converter logic in general.

Even though the converters proclaim that they have state with HasState(), cppyy doesn't respect that over multiple function calls. The string converter used for the first std::string_view is exactly the same object as for the second string view.

Do you have any implementation ideas to fix this? I'll open a separate issue to continue the discussion.

[wlav]

Issue is fixed in repo, but probably useful to add further tests.