Merge pull request #10 from GregOnNet/feature/infer-success-failure

Author: seangwright

src/result.ts

@@ -29,6 +29,20 @@ export type ResultValueOf<T> = T extends Result<infer TResultValue>
   ? TResultValue
   : unknown;
 
+/**
+ * Represents a successful Result operation.
+ */
+type ResultSuccess<TValue> = Result<TValue> & {
+  value: TValue;
+};
+
+/**
+ * Represents a failed Result operation.
+ */
+type ResultFailure<TValue, TError> = Result<TValue> & {
+  error: TError;
+};
+
 /**
  * Represents a successful or failed operation
  */
@@ -275,6 +289,36 @@ export class Result<TValue = Unit, TError = string> {
     return !this.isSuccess;
   }
 
+  /**
+   * Yields value if the result operation succeeded.
+   * Hint: Use hasValue() upfront to be sure that result operation succeeded.
+   */
+  protected get value() {
+    return this.state.value;
+  }
+
+  /**
+   * Yields error if the result operation failed.
+   * Hint: Use hasError() upfront to be sure that result operation failed.
+   */
+  protected get error() {
+    return this.state.error;
+  }
+
+  /**
+   * Checks if result operation succeeded.
+   */
+  hasValue(): this is ResultSuccess<TValue> {
+    return this.isSuccess;
+  }
+
+  /**
+   * Checks if result operation failed.
+   */
+  hasError(): this is ResultFailure<TValue, TError> {
+    return !this.isSuccess;
+  }
+
   /**
    * The internal state of the Result
    */

test/result/result.spec.ts

@@ -42,6 +42,28 @@ describe('Result', () => {
     });
   });
 
+  describe('hasValue', () => {
+    test('grants access to value when Result is in success state', () => {
+      const value = 'Alan Turing';
+      const sut = Result.success(value);
+
+      if (sut.hasValue()) {
+        expect(sut.value).toBe(value);
+      }
+    });
+  });
+
+  describe('hasError', () => {
+    test('grants access to error when Result is in error state', () => {
+      const error = 'Ouch!';
+      const sut = Result.failure(error);
+
+      if (sut.hasError()) {
+        expect(sut.error).toBe(error);
+      }
+    });
+  });
+
   describe('successIf', () => {
     describe('condition', () => {
       test('creates a successful Result if the condition is true', () => {