feat(maybe): introduce toArray function (#42)

Author: patrickmichalina

src/interfaces/maybe.interface.ts

@@ -33,6 +33,11 @@ export interface IMaybe<T> extends IMonad<T> {
    */
   valueOrUndefined(): T | undefined
 
+  /**
+   * Unwrap a Maybe with its value or return and empty list
+   */
+  toArray(): ReadonlyArray<T>
+
   /**
    * Unwrap a Maybe with a default computed value
    */

src/monads/maybe.ts

@@ -4,6 +4,7 @@ const isEmpty = <T>(value: T) => value === null || value === undefined
 const isNotEmpty = <T>(value: T) => !isEmpty(value)
 const valueOr = <T>(value?: T) => (val: NonNullable<T>) => isEmpty(value) ? val : value as NonNullable<T>
 const valueOrUndefined = <T>(value?: T) => () => isEmpty(value) ? undefined : value as NonNullable<T>
+const toArray = <T>(value?: T) => () => isEmpty(value) ? [] : Array.isArray(value) ? value : [value as NonNullable<T>]
 const valueOrCompute = <T>(value?: T) => (fn: () => NonNullable<T>) => isEmpty(value) ? fn() : value as NonNullable<T>
 const tap = <T>(value?: T) => (obj: Partial<IMaybePattern<T, void>>) => isEmpty(value) ? obj.none && obj.none() : obj.some && obj.some(value as NonNullable<T>)
 const tapNone = <T>(value?: T) => (fn: () => void) => (isEmpty(value)) && fn()
@@ -18,6 +19,7 @@ export const maybe = <T>(value?: T): IMaybe<NonNullable<T>> => {
     valueOr: valueOr(value),
     valueOrUndefined: valueOrUndefined(value),
     valueOrCompute: valueOrCompute(value),
+    toArray: toArray(value),
     tap: tap(value),
     tapNone: tapNone(value),
     tapSome: tapSome(value),

test/monads/maybe.spec.ts

@@ -347,4 +347,30 @@ describe('Maybe', () => {
       expect(maybeAString).toEqual('actual input')
     })
   })
+
+  describe('when returning an array', () => {
+    it('should handle "none" case', () => {
+      const sut = undefined as string | undefined
+      const maybeThing = maybe(sut).toArray()
+
+      expect(maybeThing).toHaveLength(0)
+      expect(maybeThing).toEqual([])
+    })
+
+    it('should handle "some" case', () => {
+      const sut = 'actual input' as string | undefined
+      const maybeThing = maybe(sut).toArray()
+
+      expect(maybeThing).toHaveLength(1)
+      expect(maybeThing).toEqual(['actual input'])
+    })
+
+    it('should handle "some" case existing array', () => {
+      const sut = ['actual input'] as ReadonlyArray<string> | undefined
+      const maybeThing = maybe(sut).toArray()
+
+      expect(maybeThing).toHaveLength(1)
+      expect(maybeThing).toEqual(['actual input'])
+    })
+  })
 })