Refactoring

README.md

@@ -1,5 +1,6 @@
 # pq-distance: Approximate Tree-Edit Distance for Node.js
 
+[![npm version](https://badge.fury.io/js/@se2p%2Fpq-distance.svg)](https://www.npmjs.com/package/@se2p/pq-distance) 
 ![CI status](https://github.com/se2p/pq-distance/actions/workflows/ci.yml/badge.svg?branch=main)
 
 Modern TypeScript implementation of pq-gram distance, an efficient approximation for tree-edit distance. Algorithm based

package.json

@@ -18,7 +18,7 @@
     "lint": "eslint src",
     "test": "jest"
   },
-  "keywords": [],
+  "keywords": ["tree-edit distance", "approximation"],
   "author": {
     "name": "Sebastian Schweikl",
     "email": "[email protected]"

src/PQGramProfile.ts

@@ -112,12 +112,12 @@ export class PQGramProfile {
         requirePositiveInteger(p, q);
 
         const profile = new PQGramProfile(p + q);
-        const workQueue: [T, Register][] = [[tree.root, new Register(p)]];
+        const workQueue: [T, Register][] = [[tree.root, Register.ofLength(p)]];
 
         while (workQueue.length > 0) {
             const [r, _anc] = workQueue.shift()!;
             const anc = _anc.shift(tree.getLabel(r));
-            let sib = new Register(q);
+            let sib = Register.ofLength(q);
 
             const children = tree.getChildren(r);
 

src/Register.ts

@@ -10,7 +10,10 @@ const NIL = Symbol("*");
  */
 type Label = string | typeof NIL;
 
-class _Register {
+/**
+ * A fixed-length shift register of labels.
+ */
+export class Register {
 
     /**
      * Current labels stored by the register.
@@ -23,11 +26,7 @@ class _Register {
      * @param contents The labels with which the register is initially filled.
      * @protected
      */
-    protected constructor(contents: Label[]) {
-        if (contents.length === 0) {
-            throw new Error("empty contents");
-        }
-
+    private constructor(contents: Label[]) {
         this._contents = contents;
     }
 
@@ -48,7 +47,7 @@ class _Register {
         const contents = [...this._contents];
         contents.push(label);
         contents.shift();
-        return new _Register(contents);
+        return new Register(contents);
     }
 
     /**
@@ -57,7 +56,7 @@ class _Register {
      * @param that The other register to concatenate with.
      */
     concat(that: Register): Register {
-        return new _Register([...this._contents, ...that._contents]);
+        return new Register([...this._contents, ...that._contents]);
     }
 
     /**
@@ -66,19 +65,13 @@ class _Register {
     toJSON(): (string | null)[] {
         return this._contents.map((l) => l === NIL ? null : l);
     }
-}
-
-/**
- * A fixed-length shift register of labels.
- */
-export class Register extends _Register {
 
     /**
      * Constructs a new, initially empty shift register which can hold the given fixed number of labels.
      * @param n The fixed length of the register.
      */
-    constructor(n: number) {
+    static ofLength(n: number) {
         requirePositiveInteger(n);
-        super(Array<Label>(n).fill(NIL));
+        return new Register(Array<Label>(n).fill(NIL));
     }
 }

test/PQGramProfile.test.ts

@@ -23,15 +23,15 @@ describe("A pq-gram profile", () => {
         it("should increase its length by 1", () => {
             const registerLength = 1;
             const p = new PQGramProfile(registerLength);
-            p.add(new Register(registerLength));
+            p.add(Register.ofLength(registerLength));
             expect(p).toHaveLength(1);
         });
 
         it("should increase its length even if it already contains the same register", () => {
             const registerLength = 1;
             const p = new PQGramProfile(registerLength);
             const times = 5;
-            const r = new Register(registerLength);
+            const r = Register.ofLength(registerLength);
             for (let i = 0; i < times; i++) {
                 p.add(r);
             }
@@ -40,7 +40,7 @@ describe("A pq-gram profile", () => {
 
         it("should throw if the register's length is incompatible", () => {
             const p = new PQGramProfile(1);
-            const r = new Register(2);
+            const r = Register.ofLength(2);
             expect(() => p.add(r)).toThrow();
         });
     });
@@ -50,7 +50,7 @@ describe("A pq-gram profile", () => {
             const registerLength = 1;
             const p = new PQGramProfile(registerLength);
             for (let i = 0; i < 5; i++) {
-                p.add(new Register(1));
+                p.add(Register.ofLength(1));
             }
             const q = new PQGramProfile(registerLength);
             expect(p.intersect(q)).toBe(0);
@@ -61,12 +61,12 @@ describe("A pq-gram profile", () => {
             const registerLength = 1;
             const p = new PQGramProfile(registerLength);
             for (let i = 0; i < 5; i++) {
-                p.add(new Register(registerLength));
+                p.add(Register.ofLength(registerLength));
             }
 
             const q = new PQGramProfile(registerLength);
             for (let i = 0; i < 3; i++) {
-                q.add(new Register(registerLength));
+                q.add(Register.ofLength(registerLength));
             }
 
             const before = {

test/Register.test.ts

@@ -4,17 +4,17 @@ import {newRegister} from "./util";
 describe("A register", () => {
     describe("that is newly constructed", () => {
         it.each([0, -1, 1.1234])("should throw an error for invalid size %d", (i) => {
-            expect(() => new Register(i)).toThrow();
+            expect(() => Register.ofLength(i)).toThrow();
         });
 
         it("should have the specified size", () => {
             const length = 42;
-            expect(new Register(42)).toHaveLength(length);
+            expect(Register.ofLength(42)).toHaveLength(length);
         });
 
         it("should be empty", () => {
             const length = 5;
-            const r = new Register(length);
+            const r = Register.ofLength(length);
             const actual = r.toJSON();
             const expected = Array(length).fill(null);
             expect(actual).toStrictEqual(expected);
@@ -23,29 +23,29 @@ describe("A register", () => {
 
     describe("that is serialized", () => {
         it("should return a fresh object", () => {
-            const r = new Register(5);
+            const r = Register.ofLength(5);
             const j = r.toJSON();
             const k = r.toJSON();
             expect(j).not.toBe(k);
         });
 
         it("should result in an array with the labels", () => {
-            const r = new Register(3).shift("foo").shift("bar");
+            const r = Register.ofLength(3).shift("foo").shift("bar");
             expect(r.toJSON()).toStrictEqual([null, "foo", "bar"]);
         });
     });
 
     describe("that is shifted", () => {
         it("should not modify the callee object", () => {
-            const r = new Register(5);
+            const r = Register.ofLength(5);
             const before = r.toJSON();
             r.shift("foo");
             const after = r.toJSON();
             expect(before).toStrictEqual(after);
         });
 
-        it("should result in a new register with the given label appended", () => {
-            const r = new Register(2);
+        it("should result in a new Register with the given label appended", () => {
+            const r = Register.ofLength(2);
             const t = r.shift("foo");
             expect(r).not.toBe(t);
             expect(t.toJSON()).toStrictEqual([null, "foo"]);
@@ -63,17 +63,17 @@ describe("A register", () => {
     });
 
     describe("that is concatenated with another register", () => {
-        it("should return a new register", () => {
-            const r = new Register(1);
-            const s = new Register(2);
+        it("should return a new Register", () => {
+            const r = Register.ofLength(1);
+            const s = Register.ofLength(2);
             const t = r.concat(s);
             expect(t).not.toBe(r);
             expect(t).not.toBe(s);
         });
 
         it("should return a register of the correct length", () => {
-            const r = new Register(1);
-            const s = new Register(2);
+            const r = Register.ofLength(1);
+            const s = Register.ofLength(2);
             const t = r.concat(s);
             expect(t).toHaveLength(r.length + s.length);
         });

test/util.ts

@@ -4,7 +4,7 @@ import {PQGramProfile, PQTree} from "../src/PQGramProfile";
 export function newRegister(r: Register | number, ...contents: (string | null)[]): Register {
     return contents.reduce(
         (r, l) => l === null ? r.shift() : r.shift(l),
-        typeof r === "number" ? new Register(r) : r);
+        typeof r === "number" ? Register.ofLength(r) : r);
 }
 
 export function newPQGramProfile(registerLength: number, contents: (string | null)[][]): PQGramProfile {