Design Decisions

Country Code Detection: Hardcoded Table vs phonenumber Crate

The check-phone-format command needs to split phone numbers into country code and local number (e.g., +79268335991 → +7-9268335991). Country codes vary in length: 1 digit (+1 US, +7 Russia), 2 digits (+44 UK), or 3 digits (+972 Israel).

Approach Chosen: Hardcoded ITU Country Code Table

rscontacts embeds a static list of ~190 ITU country codes and uses longest-prefix matching (3 digits, then 2, then 1) to detect the country code boundary.

Alternative Considered: phonenumber Crate

The phonenumber crate is a Rust port of Google’s libphonenumber. It provides:

• Phone number validation (correct digit count per country)
• Multiple formatting options (E.164, international, national)
• Region detection from number

Why We Chose the Hardcoded Table

• We only need one thing: splitting the country code from the local number. The crate would be overkill.
• Minimal dependency: the crate bundles ~2MB of per-country metadata for phone number rules we don’t use.
• Simplicity: a const array with prefix matching is trivial to understand and maintain.

When to Reconsider

If rscontacts ever needs to validate that a phone number has the correct number of digits for its country, or needs national formatting, the phonenumber crate would be the right choice.