Parsing & Validation

Constructors

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

Isin::from_bytes is the lower-level constructor: it skips whitespace-trimming and case-folding and expects an already-normalized [u8; 12]. It still runs every validation rule below. It just assumes the caller has already dealt with formatting. Prefer Isin::parse unless you’re constructing bytes programmatically (for example, in a generator or migration script).

What Isin::parse accepts

• The canonical 12-character form: CCNNNNNNNNND.
• Lowercase letters — they’re folded to uppercase automatically.
• Leading and trailing whitespace — it’s trimmed before validation.

Interior separators are not stripped: an ISIN has no conventional internal punctuation, so a character in the middle of the string that isn’t a letter or digit is reported as invalid rather than silently removed.

use ftracker_identifiers::Isin;

assert!(Isin::parse("US0378331005").is_ok());
assert!(Isin::parse("us0378331005").is_ok());   // lowercase is folded
assert!(Isin::parse("  US0378331005 ").is_ok()); // surrounding whitespace is trimmed
assert!(Isin::parse("US0378331006").is_err());   // wrong check digit

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 12 characters. (Isin::parse rejects an empty string up front.)
2. Character class — positions 1–2 accept an uppercase letter; positions 3–11 accept a digit or an uppercase letter; position 12 accepts only a digit.
3. Check digit — position 12 must match the ISO 6166 Luhn digit computed from the first 11 characters.

Each rule maps to exactly one IsinError variant; see Error Handling for the full list and how to match on it.

What it doesn’t do

Isin::parse validates shape and checksum, not existence. It cannot tell you whether a particular ISIN has actually been allocated, identifies a tradable instrument, or refers to the security you think it does. That requires a lookup against an issuing agency or market-data provider, which is out of scope for this crate.

It also does not validate the country code against the live ISO 3166-1 list (see Structure & Formats).