feat: Improve type safety of custom transform functions

src/map.ts

@@ -13,12 +13,12 @@ interface KeyValuePair<K, V> {
 /**
  * A Map implementation that supports deep equality for object keys.
  */
-export class DeepMap<K, V> extends Map<K, V> implements Comparable<DeepMap<K, V>> {
-    private readonly normalizer: Normalizer<K, V>;
-    private readonly map: Map<Normalized<K>, KeyValuePair<K, V>>;
+export class DeepMap<K, V, TxK = K, TxV = V> extends Map<K, V> implements Comparable<DeepMap<K, V, TxK, TxV>> {
+    private readonly normalizer: Normalizer<K, V, TxK, TxV>;
+    private readonly map: Map<Normalized<TxK>, KeyValuePair<K, V>>;
 
     // NOTE: This is actually a thin wrapper. We're not using super other than to drive the (typed) API contract.
-    constructor(entries?: readonly (readonly [K, V])[] | null, options: Options<K, V> = {}) {
+    constructor(entries?: readonly (readonly [K, V])[] | null, options: Options<K, V, TxK, TxV> = {}) {
         super();
         this.normalizer = new Normalizer(options);
         const transformedEntries = entries
@@ -142,11 +142,11 @@ export class DeepMap<K, V> extends Map<K, V> implements Comparable<DeepMap<K, V>
 
     // PRIVATE METHODS FOLLOW...
 
-    private normalizeKey(input: K): Normalized<K> {
+    private normalizeKey(input: K): Normalized<TxK> {
         return this.normalizer.normalizeKey(input);
     }
 
-    private normalizeValue(input: V): Normalized<V> {
+    private normalizeValue(input: V): Normalized<TxV> {
         return this.normalizer.normalizeValue(input);
     }
 }

src/normalizer.ts

@@ -11,17 +11,17 @@ type HashedObject = string;
 /**
  * Type for normalized input.
  */
-export type Normalized<T> = HashedObject | T | ReturnType<TransformFunction<T>>;
+export type Normalized<T> = HashedObject | T;
 
 /**
  * Class that normalizes object types to strings via hashing
  */
-export class Normalizer<K, V> {
+export class Normalizer<K, V, TxK, TxV> {
     private readonly objectHashOptions: ObjectHashOptions;
-    private readonly keyTransformer: TransformFunction<K>;
-    private readonly valueTransformer: TransformFunction<V>;
+    private readonly keyTransformer: TransformFunction<K, TxK>;
+    private readonly valueTransformer: TransformFunction<V, TxV>;
 
-    constructor(options: Options<K, V> = {}) {
+    constructor(options: Options<K, V, TxK, TxV> = {}) {
         const { transformer, mapValueTransformer, useToJsonTransform, ...objectHashOptions } =
             getOptionsWithDefaults(options);
         this.keyTransformer = useToJsonTransform ? Transformers.jsonSerializeDeserialize : transformer;
@@ -34,7 +34,7 @@ export class Normalizer<K, V> {
      * @param input the input to normalize
      * @returns the normalized result
      */
-    normalizeKey(input: K): Normalized<K> {
+    normalizeKey(input: K): Normalized<TxK> {
         return this.normalizeHelper(this.keyTransformer(input));
     }
 
@@ -43,7 +43,7 @@ export class Normalizer<K, V> {
      * @param input the input to normalize
      * @returns the normalized result
      */
-    normalizeValue(input: V): Normalized<V> {
+    normalizeValue(input: V): Normalized<TxV> {
         return this.normalizeHelper(this.valueTransformer(input));
     }
 

src/options.ts

@@ -6,20 +6,20 @@ import { Require } from './utils';
 /**
  * Library options
  */
-interface DeepEqualityDataStructuresOptions<K, V> {
+interface DeepEqualityDataStructuresOptions<K, V, TxK, TxV> {
     /**
      * A function that transforms Map keys or Set values prior to normalization.
      *
      * NOTE: The caller is responsible for not mutating object inputs.
      */
-    transformer?: TransformFunction<K>;
+    transformer?: TransformFunction<K, TxK>;
 
     /**
      * A function that transforms Map values prior to normalization.
      *
      * NOTE: The caller is responsible for not mutating object inputs.
      */
-    mapValueTransformer?: TransformFunction<V>;
+    mapValueTransformer?: TransformFunction<V, TxV>;
 
     /**
      * If true, objects will be JSON-serialized/deserialized into "plain" objects prior to hashing.
@@ -29,14 +29,14 @@ interface DeepEqualityDataStructuresOptions<K, V> {
     useToJsonTransform?: boolean;
 }
 
-export type Options<K, V> = ObjectHashOptions & DeepEqualityDataStructuresOptions<K, V>;
+export type Options<K, V, TxK, TxV> = ObjectHashOptions & DeepEqualityDataStructuresOptions<K, V, TxK, TxV>;
 
 /**
  * Given the specified options, resolve default values as appropriate.
  */
-export function getOptionsWithDefaults<K, V>(
-    options: Options<K, V>
-): Require<Options<K, V>, keyof DeepEqualityDataStructuresOptions<K, V>> {
+export function getOptionsWithDefaults<K, V, TxK, TxV>(
+    options: Options<K, V, TxK, TxV>
+): Require<Options<K, V, TxK, TxV>, keyof DeepEqualityDataStructuresOptions<K, V, TxK, TxV>> {
     return {
         // Default options
         algorithm: 'md5' as const, // not a cryptographic usage, who cares

src/set.ts

@@ -5,12 +5,12 @@ import { Options } from './options';
 /**
  * A Set implementation that supports deep equality for values.
  */
-export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
+export class DeepSet<V, TxV = V> extends Set<V> implements Comparable<DeepSet<V, TxV>> {
     // Just piggy-back on a DeepMap that uses null values
-    private readonly map: DeepMap<T, null>;
+    private readonly map: DeepMap<V, null, TxV, null>;
 
     // NOTE: This is actually a thin wrapper. We're not using super other than to drive the (typed) API contract.
-    constructor(values?: readonly T[] | null, options?: Options<T, null>) {
+    constructor(values?: readonly V[] | null, options?: Options<V, null, TxV, null>) {
         super();
         const transformedEntries = values ? values.map((el) => [el, null] as const) : null;
         this.map = new DeepMap(transformedEntries, options);
@@ -26,22 +26,22 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
     /**
      * Returns true if the given value is present in the set.
      */
-    override has(key: T): boolean {
-        return this.map.has(key);
+    override has(val: V): boolean {
+        return this.map.has(val);
     }
 
     /**
      * Store the given value.
      */
-    override add(val: T): this {
+    override add(val: V): this {
         this.map.set(val, null);
         return this;
     }
 
     /**
      * Deletes the specified value.
      */
-    override delete(val: T): boolean {
+    override delete(val: V): boolean {
         return this.map.delete(val);
     }
 
@@ -55,7 +55,7 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
     /**
      * Standard forEach function.
      */
-    override forEach(callbackfn: (val: T, val2: T, set: Set<T>) => void): void {
+    override forEach(callbackfn: (val: V, val2: V, set: Set<V>) => void): void {
         this.map.forEach((_mapVal, mapKey, _map) => {
             callbackfn(mapKey, mapKey, this);
         });
@@ -66,7 +66,7 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
      *
      * @yields the next value in the set
      */
-    override *[Symbol.iterator](): IterableIterator<T> {
+    override *[Symbol.iterator](): IterableIterator<V> {
         for (const [key, _val] of this.map[Symbol.iterator]()) {
             yield key;
         }
@@ -77,7 +77,7 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
      *
      * @yields the next value-value pair in the set
      */
-    override *entries(): IterableIterator<[T, T]> {
+    override *entries(): IterableIterator<[V, V]> {
         for (const val of this[Symbol.iterator]()) {
             yield [val, val];
         }
@@ -88,7 +88,7 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
      *
      * @yields the next key in the map
      */
-    override *keys(): IterableIterator<T> {
+    override *keys(): IterableIterator<V> {
         for (const val of this[Symbol.iterator]()) {
             yield val;
         }
@@ -99,7 +99,7 @@ export class DeepSet<T> extends Set<T> implements Comparable<DeepSet<T>> {
      *
      * @yields the next value in the map
      */
-    override *values(): IterableIterator<T> {
+    override *values(): IterableIterator<V> {
         yield* this.keys();
     }
 

src/transformers.ts

@@ -1,11 +1,12 @@
-export type TransformFunction<T> = (input: T) => unknown;
+export type TransformFunction<T, R> = (input: T) => R;
 
 export class Transformers {
-    static identity<T>(input: T): T {
-        return input;
+    static identity<T, R = T>(input: T): R {
+        // Just make the types happy :)
+        return input as unknown as R;
     }
 
-    static jsonSerializeDeserialize<T>(obj: T): T {
+    static jsonSerializeDeserialize<T, R = T>(obj: T): R {
         return JSON.parse(JSON.stringify(obj));
     }
 }