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Whether two names' codices rate as a match.

public static bool? Compare(string a, string b)
public static bool? Compare(ReadOnlySpan<char> a, ReadOnlySpan<char> b)

Parameters — a and b are the two names to compare, under the same rules Codex applies to a single one: any alphabetic character plus a space is accepted. The string overload forwards to the span one.

Returns — bool?. true when the two codices rate as a match, false when they do not, and null — not false — when either name holds a character Codex refuses, or when the codices' lengths differ by 3 or more UTF-8 bytes, which the algorithm declares too far apart to rate at all.

Exceptions — ArgumentNullException when a or b is null (the string overload only). A name Codex would refuse is answered with null here, as jellyfish answers None: Compare("O'Brien", "Obrien") is null.

Example — the 1977 description's own pair, and the length gap that makes a rating impossible.

using Lodestar.Text.Phonetics;

bool? byrneBoern = MatchRatingApproach.Compare("Byrne", "Boern");   // => True
bool? timTimothy = MatchRatingApproach.Compare("Tim", "Timothy");   // => null

Remarks — Compare recomputes both codices itself; a caller already holding two from Codex still calls Compare; there is no way to reach the same answer from the codices alone, because the minimum rating a comparison must clear is read from a table keyed by their combined length:

Byrne/Boern codes to BYRN/BRN, a combined length of 7 and a minimum rating of 4; cancelling shared characters from the start and then the end of what is left rates the pair at 5, which clears it. Tim/Timothy codes to TM/TMTHY, 2 and 5 characters apart — a gap of 3, so the comparison returns null before the table is even consulted.

That table, and the length it is keyed by, were measured directly against jellyfish 1.2.1 by bisection rather than assumed from a textbook. The length is counted in UTF-8 bytes, as jellyfish counts it: identical to the character count for ASCII names, and larger for anything else, so Compare("日本", "AB") is null — six bytes against two — decision 0009.

Applies to — net10.0, netstandard2.0.

See also — MatchRatingApproach, MatchRatingApproach.Codex, the phonetics index.