Merge pull request #27 from ookami-kb/memoize

lib/dfunc.dart

@@ -23,6 +23,7 @@ export 'src/map.dart';
 export 'src/map_by.dart';
 export 'src/map_indexed.dart';
 export 'src/maybe.dart';
+export 'src/memoize.dart';
 export 'src/optional.dart';
 export 'src/pipe.dart';
 export 'src/scope.dart';

lib/src/memoize.dart

@@ -0,0 +1,47 @@
+/// {@template dfunc.memoize}
+/// The `memoize` function is used to cache the results of expensive function
+/// calls and return the cached result when the same inputs are provided again.
+///
+/// Usage:
+///
+/// ```dart
+/// final memoized = memoize(expensiveFunction);
+/// final result = memoized(arg);
+/// ```
+/// {@endtemplate}
+Memoize<A, B> memoize<A, B>(
+  A Function(B lastArgument) f, {
+  int? capacity,
+}) =>
+    Memoize<A, B>(f, capacity: capacity);
+
+/// {@macro dfunc.memoize}
+class Memoize<A, B> {
+  /// {@macro dfunc.memoize}
+  Memoize(this._f, {int? capacity}) : _capacity = capacity;
+
+  final Map<B, A> _cache = {};
+
+  final A Function(B lastArgument) _f;
+  final int? _capacity;
+
+  /// Returns the cached value for the argument [b] if it exists, otherwise
+  /// computes the value using the function [_f] and caches it.
+  A call(B b) {
+    if (_cache.containsKey(b)) return _cache[b] as A;
+
+    final value = _f(b);
+    _cache[b] = value;
+
+    // ignore: avoid-non-null-assertion, checked for null
+    if (_capacity != null && _cache.length > _capacity!) {
+      _cache.remove(_cache.keys.first);
+    }
+
+    return value;
+  }
+
+  /// Clears the memoization cache, subsequent call with the same argument will
+  /// recompute the value.
+  void reset() => _cache.clear();
+}

pubspec.yaml

@@ -8,5 +8,5 @@ environment:
 
 dev_dependencies:
   melos: ^3.0.1
-  mews_pedantic: ^0.23.0
+  mews_pedantic: ^0.26.0
   test: ^1.16.2

test/intersperse_test.dart

@@ -1,3 +1,5 @@
+// ignore_for_file: avoid-unnecessary-collections, avoid-duplicate-collection-elements
+
 import 'package:dfunc/dfunc.dart';
 import 'package:test/test.dart';
 

test/memoize_test.dart

@@ -0,0 +1,81 @@
+// ignore_for_file: avoid-duplicate-test-assertions, avoid-duplicate-collection-elements
+
+import 'package:dfunc/dfunc.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('memoize', () {
+    int counter = 0;
+
+    final memoized = memoize((int arg) {
+      counter++;
+
+      return arg * 2;
+    });
+
+    expect(memoized(1), 2);
+    expect(counter, 1);
+
+    // Doesn't call the function again.
+    expect(memoized(1), 2);
+    expect(counter, 1);
+
+    // Calls the function for a different argument.
+    expect(memoized(2), 4);
+    expect(counter, 2);
+
+    // Doesn't call the function again.
+    expect(memoized(1), 2);
+    expect(counter, 2);
+  });
+
+  test('memoize with limited capacity', () {
+    int counter = 0;
+
+    final memoized = memoize(capacity: 1, (int arg) {
+      counter++;
+
+      return arg * 2;
+    });
+
+    expect(memoized(1), 2);
+    expect(counter, 1);
+
+    // Doesn't call the function again.
+    expect(memoized(1), 2);
+    expect(counter, 1);
+
+    // Calls the function for a different argument.
+    expect(memoized(2), 4);
+    expect(counter, 2);
+
+    // Calls the function again if capacity exceeded.
+    expect(memoized(1), 2);
+    expect(counter, 3);
+  });
+
+  test('memoize async', () async {
+    int counter = 0;
+
+    final memoized = memoize((int arg) async {
+      await Future<void>.delayed(Duration.zero);
+      counter++;
+
+      return arg * 2;
+    });
+
+    expect(await memoized(1), 2);
+    expect(counter, 1);
+
+    // Doesn't call the function again.
+    expect(await memoized(1), 2);
+    expect(counter, 1);
+
+    // Calls the function one time for a different argument.
+    expect(
+      await Future.wait([memoized(2), memoized(2), memoized(2)]),
+      [4, 4, 4],
+    );
+    expect(counter, 2);
+  });
+}