Add RcMap.keys and MutableHashMap.keys lookup functions (#3559)

Co-authored-by: Tim <hello@timsmart.co>
Co-authored-by: Tim Smart <tim.smart@arisechurch.com>

.changeset/violet-suns-chew.md

@@ -0,0 +1,26 @@
+---
+"effect": minor
+---
+
+Added `RcMap.keys` and `MutableHashMap.keys`.
+
+These functions allow you to get a list of keys currently stored in the underlying hash map.
+
+```ts
+const map = MutableHashMap.make([["a", "a"], ["b", "b"], ["c", "c"]])
+const keys = MutableHashMap.keys(map) // ["a", "b", "c"]
+```
+
+```ts
+Effect.gen(function* () {
+  const map = yield* RcMap.make({
+    lookup: (key) => Effect.succeed(key)
+  })
+
+  yield* RcMap.get(map, "a")
+  yield* RcMap.get(map, "b")
+  yield* RcMap.get(map, "c")
+
+  const keys = yield* RcMap.keys(map) // ["a", "b", "c"]
+})
+```

packages/effect/src/MutableHashMap.ts

@@ -159,6 +159,18 @@ export const get: {
   return getFromBucket(self, bucket, key)
 })
 
+/**
+ * @since 3.8.0
+ * @category elements
+ */
+export const keys = <K, V>(self: MutableHashMap<K, V>): Array<K> => {
+  const keys: Array<K> = []
+  for (const [key] of self) {
+    keys.push(key)
+  }
+  return keys
+}
+
 const getFromBucket = <K, V>(
   self: MutableHashMap<K, V>,
   bucket: NonEmptyArray<readonly [K & Equal.Equal, V]>,

packages/effect/src/RcMap.ts

@@ -101,3 +101,9 @@ export const get: {
   <K>(key: K): <A, E>(self: RcMap<K, A, E>) => Effect.Effect<A, E, Scope.Scope>
   <K, A, E>(self: RcMap<K, A, E>, key: K): Effect.Effect<A, E, Scope.Scope>
 } = internal.get
+
+/**
+ * @since 3.8.0
+ * @category combinators
+ */
+export const keys: <K, A, E>(self: RcMap<K, A, E>) => Effect.Effect<Array<K>, E> = internal.keys

packages/effect/src/internal/rcMap.ts

@@ -211,3 +211,11 @@ export const get: {
     )
   }
 )
+
+/** @internal */
+export const keys = <K, A, E>(self: RcMap.RcMap<K, A, E>): Effect<Array<K>> => {
+  const impl = self as RcMapImpl<K, A, E>
+  return core.suspend(() =>
+    impl.state._tag === "Closed" ? core.interrupt : core.succeed(MutableHashMap.keys(impl.state.map))
+  )
+}

packages/effect/test/MutableHashMap.test.ts

@@ -174,6 +174,19 @@ describe("MutableHashMap", () => {
     )
   })
 
+  it("keys", () => {
+    const map = pipe(
+      HM.empty<Key, Value>(),
+      HM.set(key(0, 0), value(0, 0)),
+      HM.set(key(1, 1), value(1, 1))
+    )
+
+    expect(HM.keys(map)).toStrictEqual([
+      key(0, 0),
+      key(1, 1)
+    ])
+  })
+
   it("modifyAt", () => {
     const map = pipe(
       HM.empty<Key, Value>(),

packages/effect/test/RcMap.test.ts

@@ -124,4 +124,17 @@ describe("RcMap", () => {
       // no failure means a hit
       assert.strictEqual(yield* RcMap.get(map, new Key({ id: 1 })), 1)
     }))
+
+  it.scoped("keys lookup", () =>
+    Effect.gen(function*() {
+      const map = yield* RcMap.make({
+        lookup: (key: string) => Effect.succeed(key)
+      })
+
+      yield* RcMap.get(map, "foo")
+      yield* RcMap.get(map, "bar")
+      yield* RcMap.get(map, "baz")
+
+      assert.deepStrictEqual(yield* RcMap.keys(map), ["foo", "bar", "baz"])
+    }))
 })