How do I specify the type of function pointers to jitclass member function

Numba Support: How do I do ...?
1

I’m trying to write a jitclass which has a function pointer which will select which member function to call. I’m currently stuck at what type annotation I should put for the function pointer, which points to a member function. A minimum example is shown below:

nb.experimental.jitclass
class Foo:
    a: float
    f: <what type to put here?>

    def __init__(self, a):
        if a > 1e-6:
            self.f = func1
        else:
            self.f = func2

    def func1(self, x):
        return x * x

    def func2(self, x):
        return x * x + self.a

This issue is somewhat similar to numba.discourse.group/t/function-pointer-inside-a-jitclass/903 from 2 years ago. For that issue, because both pointed functions rely no internal state of the jitclass, we can do a workaround by moving them outside the jitclass:

nb.experimental.jitclass
class Foo:
    a: float
    f: nb.float64(nb.float64).as_type()

    def __init__(self, a):
        if a > 1e-6:
            self.f = func1
        else:
            self.f = func2

@nb.njit
def func1(x):
    return x * x

@nb.njit
def func2(x):
    return x + x

foo = Foo(0)
print(foo.f(5))