feat: add tap methods to Result (#188)

Author: patrickmichalina

src/result/result.interface.ts

@@ -20,6 +20,21 @@ export interface IResult<T, E> {
   mapFail<M>(fn: (err: E) => M): IResult<T, M>
   flatMap<M>(fn: (val: T) => IResult<M, E>): IResult<M, E>
 
+  /**
+   * Execute functions with side-effects.
+   */
+  tap(val: Partial<IResultMatchPattern<T, E, void>>): void
+
+  /**
+   * Execute a function with side-effects when maybe is a Fail.
+   */
+  tapFail(f: (val: E) => void): void
+
+  /**
+   * Execute a function with side-effects when maybe is an Ok.
+   */
+  tapOk(f: (val: T) => void): void
+
   /**
    * Convert Ok result into Fail using projected value from Ok
    */

src/result/result.spec.ts

@@ -199,4 +199,58 @@ describe('result', () => {
       expect(sut.unwrapFail().message).toEqual('error msg')
     })
   })
+
+  describe('tap', () => {
+    it('should tap.ok', done => {
+      const sut = ok(1)
+      
+      sut.tap({
+        ok: num => {
+          expect(num).toEqual(1)
+          done()
+        },
+        fail: done
+      })
+    })
+
+    it('should tap.ok', done => {
+      const sut = fail<number, string>('failed')
+      
+      sut.tap({
+        fail: str => {
+          expect(str).toEqual('failed')
+          done()
+        },
+        ok: done
+      })
+    })
+
+    it('should tapOk', done => {
+      const sut = ok<number, string>(1)
+      
+      sut.tapOk(num => {
+        expect(num).toEqual(1)
+        done()
+      })
+
+      sut.tapFail(() => {
+        expect(true).toBeFalsy()
+        done()
+      })
+    })
+
+    it('should tapFail', done => {
+      const sut = fail<number, string>('failed')
+      
+      sut.tapFail(err => {
+        expect(err).toEqual('failed')
+        done()
+      })
+
+      sut.tapOk(() => {
+        expect(true).toBeFalsy()
+        done()
+      })
+    })
+  })
 })

src/result/result.ts

@@ -3,12 +3,10 @@ import { IResultMatchPattern, IResult } from './result.interface'
 
 export abstract class Result<TOk, TFail> implements IResult<TOk, TFail> {
   public static ok<TOk, TFail>(value: TOk): IResult<TOk, TFail> {
-    // eslint-disable-next-line @typescript-eslint/no-use-before-define
     return new OkResult<TOk, TFail>(value)
   }
 
   public static fail<TOk, TFail>(value: TFail): IResult<TOk, TFail> {
-    // eslint-disable-next-line @typescript-eslint/no-use-before-define
     return new FailResult<TOk, TFail>(value)
   }
 
@@ -25,6 +23,9 @@ export abstract class Result<TOk, TFail> implements IResult<TOk, TFail> {
   abstract flatMap<M>(fn: (val: TOk) => IResult<M, TFail>): IResult<M, TFail>
   abstract toFailWhenOk(fn: (val: TOk) => TFail): IResult<TOk, TFail>
   abstract toFailWhenOkFrom(val: TFail): IResult<TOk, TFail>
+  abstract tap(val: IResultMatchPattern<TOk, TFail, void>): void
+  abstract tapOk(f: (val: TOk) => void): void
+  abstract tapFail(f: (val: TFail) => void): void
 }
 
 export class OkResult<TOk, TFail> extends Result<TOk, TFail> {
@@ -83,6 +84,16 @@ export class OkResult<TOk, TFail> extends Result<TOk, TFail> {
   toFailWhenOkFrom(val: TFail): IResult<TOk, TFail> {
     return Result.fail(val)
   }
+
+  tap(val: Partial<IResultMatchPattern<TOk, TFail, void>>): void {
+    typeof val.ok === 'function' && val.ok(this.successValue)
+  }
+
+  tapOk(fn: (val: TOk) => void): void {
+    fn(this.successValue)
+  }
+
+  tapFail(): void { }
 }
 
 export class FailResult<TOk, TFail> extends Result<TOk, TFail> implements IResult<TOk, TFail>  {
@@ -141,4 +152,14 @@ export class FailResult<TOk, TFail> extends Result<TOk, TFail> implements IResul
   toFailWhenOkFrom(val: TFail): IResult<TOk, TFail> {
     return Result.fail(val)
   }
+
+  tap(val: Partial<IResultMatchPattern<TOk, TFail, void>>): void {
+    typeof val.fail === 'function' && val.fail(this.failureValue)
+  }
+
+  tapOk(): void { }
+
+  tapFail(fn: (val: TFail) => void): void {
+    fn(this.failureValue)
+  }
 }