alt Hacker NewsObviously the pseudo code leaves to the imagination, but what benefits does this give you? Are you checking that it is 10-digits? Are you allowing for + symbols for the international codes?
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You have functions
void callNumber(string phoneNumber);
void associatePhoneNumber(string phoneNumber, Person person);
Person lookupPerson(string phoneNumber);
Provider getProvider(string phoneNumber);
PhoneNumber PhoneNumber(string phoneNumber);
void callNumber(PhoneNumber phoneNumber);
void associatePhoneNumber(PhoneNumber phoneNumber, Person person);
Person lookupPerson(PhoneNumber phoneNumber);
Provider getProvider(PhoneNumber phoneNumber);
That's going to be up to the business building the logic. Ideally those assumptions are clearly encoded in an easily readable manner but at the very least they should be captured somewhere code adjacent (even if it's just a comment and the block of logic to enforce those restraints).
If you are not checking that the phone number is 10 digits (or whatever the rules are for the phone number for your use case), it is absolutely pointless. But why would you not?
And parentheses. And spaces (that may, or may not, be trimmed). And all kind of unicode equivalent characters, that might have to be canonicalized. Why not treat it as a byte buffer anyway.
Can't pass a PhoneNumber to a function expecting an EmailAddress, for one, or mix up the order of arguments in a function that may otherwise just take two or more strings