'Get the compiled dispatcher implementing the attribute for
the given formal signature.'

@classmethod
def _get_dispatcher(cls, context, typ, attr, sig_args, sig_kws):

    cache_key = (context, typ, attr)
    try:
        disp = cls._impl_cache[cache_key]
    except KeyError:
        pyfunc = cls._overload_func(*sig_args, **sig_kws)
        if (pyfunc is None):
            cls._impl_cache[cache_key] = None
            return
        from numba import jit
        disp = cls._impl_cache[cache_key] = jit(nopython=True)(pyfunc)
    return disp
