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BkTree(metric)

Builds an empty tree over a metric of the caller's own, for the one case the four factories do not reach.

public BkTree(Func<string, string, int> metric)

Parameters — metric is the distance the tree indexes on. It must satisfy the triangle inequality, be symmetric, and return 0 only for equal inputs — the same three properties OverLevenshtein, OverDamerauLevenshtein, OverIndel and OverHamming already carry proof for. Nothing here checks it — it cannot be, from a delegate — so the caller owns the precondition, and a metric that violates it returns an incomplete result set rather than throwing.

Returns — an empty BkTree.

Example — a metric none of the four factories offer.

using Lodestar.Text.Distances;
using Lodestar.Text.Indexing;

BkTree tree = new((a, b) => Levenshtein.Distance(a, b));
tree.AddRange(["book", "boo", "cook"]);
int found = tree.WithinDistance("bok", 1).Count;   // => 2

Remarks — reach for this constructor when the four factories do not name the distance you need — a domain-specific edit cost, a phonetic distance, anything satisfying the same inequality — and bring the proof with it: AdmissibleMetricTests in the test suite shows the shape that proof takes, an exhaustive sweep over every triple of words up to a bounded length and alphabet, not a sample.

Runs on both target frameworks: net10.0, netstandard2.0.

See also — BkTree, BkTree.OverLevenshtein.