Is overloading broken in cppclass Cython/C++ definitions?

Question

Cython documentation shows how to declare existing C++ classes with overloaded methods.

However, if I define my own cppclass with an overloaded method ...

cdef cppclass point:
    float x, y

    point():
        this.x = 0
        this.y = 0

    float sum():
        return this.x + this.y

    float sum(int z): # COMPILE ERROR
        return this.x + this.y + z

... I get

Function signature does not match previous declaration

Overloading the constructor gives the same error there:

cdef cppclass point:
    float x, y

    point():
        this.x = 0
        this.y = 0

    point(float X, float Y): # COMPILE ERROR
        this.x = X
        this.y = Y

    float sum():
        return this.x + this.y

Am I doing this incorrectly, or is this feature missing?

Update: Default arguments seem to be unusable too:

cdef cppclass point:
    float x, y

    point(float X=0, float Y=0):
        this.x = X
        this.y = Y

    float sum():
        return this.x + this.y

cdef float use_point():
    cdef point p
    p = point(1, 2)
    return p.sum()

... passes Cython, but gets tripped up by the C++ compiler ("wrong number of arguments")

Answer 1

As I said in a comment: this clearly is a bug/unsupported feature, and so it's probably much more useful to report it on the Cython issues list on github than post it here.

However, if you're interested in a hacky short-term workround then the following works:

    float sum(...):
        return this.x + this.y

    float sum2 "sum"(int z):
        return this.x + this.y + z

# A test function to prove it
def test():
    cdef point pt
    a = pt.sum()
    b = pt.sum(3)

    return a,b # returns (0.0, 3.0)

This uses 2 tricks

1. Cython lets you specify an "actual" name for the function by putting it in quotes. Thus float sum2 "sum"(int z): ends up calling the function sum, but it tricks Cython so that it doesn't register than you've reused the same name. The automatic C++ type deduction will work correctly though.

2. ... (i.e. C varargs) will match anything but it given the lowest priority by the C++ type deduction mechanism. Therefore sum(3) picks sum(int) ahead of sum(...). This also stops Cython thinking too hard about the types and leaves it up to C++ (as desired). The downside is that it won't tell you if you pass a huge nonsensical list of arguments but will just silently call the (...) version.

This hack doesn't work for constructors, and doesn't look easy to make work for constructors.