Merge pull request #4 from surol/updatable-context-values

Updatable context values

Author: surol

package.json

@@ -21,6 +21,7 @@
   "dependencies": {
     "a-iterable": "^2.4.2",
     "call-thru": "^2.5.2",
+    "fun-events": "^5.0.3",
     "tslib": "^1.10.0"
   },
   "devDependencies": {

src/context-key-error.ts

@@ -0,0 +1,24 @@
+import { ContextKey } from './context-key';
+
+/**
+ * An error indicating the absence of context value with the given key.
+ */
+export class ContextKeyError extends Error {
+
+  /**
+   * A missing value key.
+   */
+  readonly key: ContextKey<any, any, any>;
+
+  /**
+   * Constructs an invalid context key error.
+   *
+   * @param key  Missing value key.
+   * @param message  Arbitrary error message.
+   */
+  constructor(key: ContextKey<any, any, any>, message: string = `There is no value with key ${key}`) {
+    super(message);
+    this.key = key;
+  }
+
+}

src/context-key.ts

@@ -102,7 +102,7 @@ export interface ContextValueOpts<Ctx extends ContextValues, Value, Src, Seed> {
   /**
    * Handles missing context value.
    *
-   * It can be called to prefer a fallback value over default one specified by the value key.
+   * It can be called to prefer a fallback value over the default one specified in the value key.
    *
    * @param defaultProvider  Default value provider. It is called unless a fallback value is specified.
    * If it returns a non-null/non-undefined value, then the returned value will be associated with the context key.
@@ -124,7 +124,7 @@ export abstract class ContextSeedKey<Src, Seed> extends ContextKey<Seed, Src, Se
    *
    * @param key  A key of context value having its sources associated with this key.
    */
-  protected constructor(key: ContextKey<any, Src>) {
+  constructor(key: ContextKey<any, Src>) {
     super(`${key.name}:seed`);
   }
 

src/context-registry.spec.ts

@@ -1,7 +1,7 @@
 import { AIterable } from 'a-iterable';
 import { ContextRegistry } from './context-registry';
 import { ContextValues } from './context-values';
-import { MultiContextKey, SingleContextKey } from './simple-context-key';
+import { SingleContextKey } from './simple-context-key';
 import Mock = jest.Mock;
 
 describe('ContextRegistry', () => {
@@ -49,182 +49,6 @@ describe('ContextRegistry', () => {
     });
   });
 
-  describe('Single value', () => {
-    it('provides value', () => {
-
-      const value = 'test value';
-
-      mockProvider.mockReturnValue(value);
-
-      expect(values.get(key)).toBe(value);
-    });
-    it('throws if there is neither default nor fallback value', () => {
-      expect(() => values.get(new SingleContextKey(key.name))).toThrowError();
-      expect(() => values.get(new SingleContextKey(key.name), {})).toThrowError();
-    });
-    it('provides fallback value is there is no provider', () => {
-      expect(values.get(new SingleContextKey<string>(key.name), { or: 'fallback' })).toBe('fallback');
-    });
-    it('provides default value if provider did not provide any value', () => {
-
-      const defaultValue = 'default';
-      const keyWithDefaults = new SingleContextKey(key.name, { byDefault: () => defaultValue });
-
-      registry.provide({ a: keyWithDefaults, is: null });
-
-      expect(values.get(keyWithDefaults)).toBe(defaultValue);
-    });
-    it('provides default value if there is no provider', () => {
-      expect(values.get(new SingleContextKey<string>(key.name, { byDefault: () => 'default' }))).toBe('default');
-    });
-    it('prefers fallback value over default one', () => {
-      expect(values.get(new SingleContextKey<string>(key.name, { byDefault: () => 'default' }), { or: 'fallback' }))
-          .toBe('fallback');
-    });
-    it('prefers default value if fallback one is absent', () => {
-      expect(values.get(new SingleContextKey<string>(key.name, { byDefault: () => 'default' }), {}))
-          .toBe('default');
-    });
-    it('prefers `null` fallback value over key one', () => {
-      expect(values.get(new SingleContextKey<string>(key.name, { byDefault: () => 'default' }), { or: null }))
-          .toBeNull();
-    });
-    it('prefers `undefined` fallback value over key one', () => {
-      expect(values.get(new SingleContextKey<string>(key.name, { byDefault: () => 'default' }), { or: undefined }))
-          .toBeUndefined();
-    });
-    it('caches the value', () => {
-
-      const value = 'value';
-
-      mockProvider.mockReturnValue(value);
-
-      expect(values.get(key)).toBe(value);
-      expect(values.get(key)).toBe(value);
-
-      expect(mockProvider).toHaveBeenCalledTimes(1);
-    });
-    it('caches default value', () => {
-
-      const value = 'default value';
-      const defaultProviderSpy = jest.fn(() => value);
-      const keyWithDefault = new SingleContextKey('key-with-default', { byDefault: defaultProviderSpy });
-
-      expect(values.get(keyWithDefault)).toBe(value);
-      expect(values.get(keyWithDefault)).toBe(value);
-      expect(defaultProviderSpy).toHaveBeenCalledTimes(1);
-    });
-    it('does not cache fallback value', () => {
-
-      const value1 = 'value1';
-      const value2 = 'value2';
-
-      expect(values.get(key, { or: value1 })).toBe(value1);
-      expect(values.get(key, { or: value2 })).toBe(value2);
-    });
-    it('rebuilds the value in another context', () => {
-
-      const value1 = 'value1';
-      const value2 = 'value2';
-
-      mockProvider.mockReturnValue(value1);
-      expect(values.get(key)).toBe(value1);
-
-      const values2 = registry.newValues();
-
-      mockProvider.mockReturnValue(value2);
-      expect(values.get(key)).toBe(value1);
-      expect(values2.get(key)).toBe(value2);
-
-      expect(mockProvider).toHaveBeenCalledTimes(2);
-    });
-  });
-
-  describe('Multi-value', () => {
-
-    let multiKey: MultiContextKey<string>;
-
-    beforeEach(() => {
-      multiKey = new MultiContextKey('values');
-    });
-
-    it('is associated with empty array by default', () => {
-      expect(values.get(multiKey)).toEqual([]);
-    });
-    it('is associated with empty array if providers did not return any values', () => {
-      registry.provide({ a: multiKey, is: null });
-      registry.provide({ a: multiKey, is: undefined });
-
-      expect(values.get(multiKey)).toEqual([]);
-    });
-    it('is associated with default value if there is no provider', () => {
-
-      const defaultValue = ['default'];
-      const keyWithDefaults = new MultiContextKey('key', { byDefault: () => defaultValue });
-
-      expect(values.get(keyWithDefaults)).toEqual(defaultValue);
-    });
-    it('is associated with default value if providers did not return any values', () => {
-
-      const defaultValue = ['default'];
-      const keyWithDefaults = new MultiContextKey('key', { byDefault: () => defaultValue });
-
-      registry.provide({ a: keyWithDefaults, is: null });
-      registry.provide({ a: keyWithDefaults, is: undefined });
-
-      expect(values.get(keyWithDefaults)).toEqual(defaultValue);
-    });
-    it('is associated with provided values array', () => {
-      registry.provide({ a: multiKey, is: 'a' });
-      registry.provide({ a: multiKey, is: undefined });
-      registry.provide({ a: multiKey, is: 'c' });
-
-      expect(values.get(multiKey)).toEqual(['a', 'c']);
-    });
-    it('is associated with value', () => {
-      registry.provide({ a: multiKey, is: 'value' });
-
-      expect(values.get(multiKey)).toEqual(['value']);
-    });
-    it('throws if there is no default value', () => {
-      expect(() => values.get(new MultiContextKey(multiKey.name, { byDefault: () => null }))).toThrowError();
-    });
-    it('is associated with empty array by default', () => {
-      expect(values.get(new MultiContextKey(multiKey.name))).toEqual([]);
-    });
-    it('is associated with default value is there is no value', () => {
-      expect(values.get(new MultiContextKey<string>(multiKey.name), { or: ['default'] }))
-          .toEqual(['default']);
-    });
-    it('is associated with key default value is there is no value', () => {
-      expect(values.get(new MultiContextKey<string>(multiKey.name, { byDefault: () => ['default'] })))
-          .toEqual(['default']);
-    });
-    it('prefers fallback value over default one', () => {
-      expect(values.get(
-          new MultiContextKey<string>(
-              multiKey.name,
-              { byDefault: () => ['key', 'default'] }
-          ),
-          { or: ['explicit', 'default'] }
-      )).toEqual(['explicit', 'default']);
-    });
-    it('prefers `null` fallback value over default one', () => {
-      expect(values.get(
-          new MultiContextKey<string>(multiKey.name, { byDefault: () => ['key', 'default'] }),
-          { or: null }
-      )).toBeNull();
-    });
-    it('prefers `undefined` fallback value over default one', () => {
-      expect(values.get(new MultiContextKey<string>(
-          multiKey.name,
-          { byDefault: () => ['key', 'default'] }
-          ),
-          { or: undefined }
-      )).toBeUndefined();
-    });
-  });
-
   describe('Providers combination', () => {
 
     let provider2Spy: Mock;

src/context-registry.ts

@@ -7,6 +7,7 @@ import { ContextRef, ContextRequest } from './context-ref';
 import { ContextSeeder, ContextSeeds } from './context-seeder';
 import { contextValueSpec, ContextValueSpec } from './context-value-spec';
 import { ContextValues } from './context-values';
+import { ContextKeyError } from './context-key-error';
 
 type SeedFactory<Ctx extends ContextValues, Seed> = (this: void, context: Ctx) => Seed;
 
@@ -53,13 +54,15 @@ export class ContextRegistry<Ctx extends ContextValues = ContextValues> {
    * @typeparam Src  Source value type.
    * @typeparam Seed  Value seed type.
    * @param spec  Context value specifier.
+   *
+   * @returns A function that removes the given context value specifier when called.
    */
-  provide<Deps extends any[], Src, Seed>(spec: ContextValueSpec<Ctx, any, Deps, Src, Seed>): void {
+  provide<Deps extends any[], Src, Seed>(spec: ContextValueSpec<Ctx, any, Deps, Src, Seed>): () => void {
 
     const { a: { [ContextKey__symbol]: { seedKey } }, by } = contextValueSpec(spec);
     const [seeder] = this._seeding<Src, Seed>(seedKey);
 
-    seeder.provide(by);
+    return seeder.provide(by);
   }
 
   /**
@@ -182,7 +185,7 @@ export class ContextRegistry<Ctx extends ContextValues = ContextValues> {
               const defaultValue = defaultProvider();
 
               if (defaultValue == null) {
-                throw new Error(`There is no value with key ${key}`);
+                throw new ContextKeyError(key);
               }
 
               return defaultValue;

src/context-seeder.ts

@@ -23,8 +23,10 @@ export interface ContextSeeder<Ctx extends ContextValues, Src, Seed> {
    * Provides context value.
    *
    * @param provider  Context value provider.
+   *
+   * @returns A function that removes the given context value `provider` when called.
    */
-  provide(provider: ContextValueProvider<Ctx, Src>): void;
+  provide(provider: ContextValueProvider<Ctx, Src>): () => void;
 
   /**
    * Creates context value seed for target `context`.