Parsing & Validation

Constructors

• CountryCode::parse and CountryCode::new accept two character strings, in any ASCII case, trimmed of surrounding whitespace.
• CountryCode::from_bytes accepts exactly two pre normalized uppercase ASCII bytes.
• FromStr and TryFrom<&str> behave like parse, for use in generic code.

CountryCode::new is a plain alias for CountryCode::parse. FromStr and TryFrom<&str> both delegate to it too, so "...".parse::<CountryCode>() and CountryCode::try_from("...") behave identically to calling CountryCode::parse directly.

CountryCode::from_bytes is the lower level constructor. It skips whitespace trimming and case folding and expects an already normalized [u8; 2]. It still runs every validation rule below. Prefer CountryCode::parse unless you are constructing bytes programmatically (for example, in a generator or a migration script).

What CountryCode::parse accepts

• The canonical two character form.
• Lowercase letters. They are folded to uppercase automatically.
• Leading and trailing whitespace. It is trimmed before validation.

Interior separators are not stripped. A country code has no internal punctuation, so a character that is not a letter is reported as invalid rather than silently removed.

use ftracker_identifiers::CountryCode;

assert!(CountryCode::parse("US").is_ok());
assert!(CountryCode::parse("us").is_ok());    // lowercase is folded
assert!(CountryCode::parse("  BR ").is_ok()); // surrounding whitespace is trimmed
assert!(CountryCode::parse("ZZ").is_err());   // well formed but not assigned

Validation rules

The string based constructors run the following rules, in this order:

1. Length: after surrounding whitespace is trimmed, the input must contain exactly two characters. (CountryCode::parse rejects an empty string first.)
2. Character class: both positions must be an uppercase ASCII letter (A to Z).
3. Assignment: the two letters together must be a code that ISO 3166-1 officially assigns.

Rule 3 is checked against the embedded bitmap with a single array index and a single bit test. There is no heap allocation and no runtime initialization. Each rule maps to exactly one CountryCodeError variant. See Error Handling for the full list and how to match on it.

What it doesn’t do

CountryCode::parse validates shape and membership, not meaning. It cannot tell you which country a code names (the names are not embedded, see Structure & Formats), and it does not map between the alpha-2 code and the alpha-3 or numeric forms.