initial commit: scaffolding

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diff --git a/node_modules/rxjs/src/internal/operators/distinctUntilKeyChanged.ts b/node_modules/rxjs/src/internal/operators/distinctUntilKeyChanged.ts
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+import { distinctUntilChanged } from './distinctUntilChanged';
+import { MonoTypeOperatorFunction } from '../types';
+
+export function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>;
+export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T>;
+
+/**
+ * Returns an Observable that emits all items emitted by the source Observable that
+ * are distinct by comparison from the previous item, using a property accessed by
+ * using the key provided to check if the two items are distinct.
+ *
+ * If a comparator function is provided, then it will be called for each item to
+ * test for whether that value should be emitted or not.
+ *
+ * If a comparator function is not provided, an equality check is used by default.
+ *
+ * ## Examples
+ *
+ * An example comparing the name of persons
+ *
+ * ```ts
+ * import { of, distinctUntilKeyChanged } from 'rxjs';
+ *
+ * of(
+ *   { age: 4, name: 'Foo' },
+ *   { age: 7, name: 'Bar' },
+ *   { age: 5, name: 'Foo' },
+ *   { age: 6, name: 'Foo' }
+ * ).pipe(
+ *   distinctUntilKeyChanged('name')
+ * )
+ * .subscribe(x => console.log(x));
+ *
+ * // displays:
+ * // { age: 4, name: 'Foo' }
+ * // { age: 7, name: 'Bar' }
+ * // { age: 5, name: 'Foo' }
+ * ```
+ *
+ * An example comparing the first letters of the name
+ *
+ * ```ts
+ * import { of, distinctUntilKeyChanged } from 'rxjs';
+ *
+ * of(
+ *   { age: 4, name: 'Foo1' },
+ *   { age: 7, name: 'Bar' },
+ *   { age: 5, name: 'Foo2' },
+ *   { age: 6, name: 'Foo3' }
+ * ).pipe(
+ *   distinctUntilKeyChanged('name', (x, y) => x.substring(0, 3) === y.substring(0, 3))
+ * )
+ * .subscribe(x => console.log(x));
+ *
+ * // displays:
+ * // { age: 4, name: 'Foo1' }
+ * // { age: 7, name: 'Bar' }
+ * // { age: 5, name: 'Foo2' }
+ * ```
+ *
+ * @see {@link distinct}
+ * @see {@link distinctUntilChanged}
+ *
+ * @param key String key for object property lookup on each item.
+ * @param compare Optional comparison function called to test if an item is distinct
+ * from the previous item in the source.
+ * @return A function that returns an Observable that emits items from the source
+ * Observable with distinct values based on the key specified.
+ */
+export function distinctUntilKeyChanged<T, K extends keyof T>(
+  key: K,
+  compare?: (x: T[K], y: T[K]) => boolean
+): MonoTypeOperatorFunction<T> {
+  return distinctUntilChanged((x: T, y: T) => (compare ? compare(x[key], y[key]) : x[key] === y[key]));
+}