shared external funcs in cairo

contract.cairo

%lang starknet

from openzeppelin.access.ownable import Ownable

# this import brings public function from ownable_external.cairo
# into this contract; the OWNABLE is just a placeholder, because
# something has to be imported, Cairo doesn't support
# `from foo import *` nor `import foo`
from contracts.ownable_external import OWNABLE

@constructor
func constructor{
        syscall_ptr: felt*,
        pedersen_ptr: HashBuiltin*,
        range_check_ptr
    }(owner : felt):
    Ownable.initializer(owner)
    return ()
end

@external
func my_func():
end

ownable_external.cairo

%lang starknet

from openzeppelin.access.ownable import Ownable

const OWNABLE = 1

@external
func transferOwnership{
        syscall_ptr: felt*,
        pedersen_ptr: HashBuiltin*,
        range_check_ptr
    }(newOwner: felt):
    Ownable.transfer_ownership(newOwner)
    return ()
end

@external
func renounceOwnership{
        syscall_ptr: felt*,
        pedersen_ptr: HashBuiltin*,
        range_check_ptr
    }():
    Ownable.renounce_ownership()
    return ()
end