feat: narrow down Result type after isOk or isErr

yifanwww · Apr 14, 2024 · 01058c2 · 01058c2
1 parent a8e4b3c
commit 01058c2
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Showing 2 changed files with 4 additions and 4 deletions.
diff --git a/src/result.ts b/src/result.ts
@@ -56,7 +56,7 @@ export class RustlikeResult<T, E> implements Result<T, E> {
      *
      * ref: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_ok
      */
-    isOk(): boolean {
+    isOk(): this is Result<T, never> {
         return this._type === 'ok';
     }
 
@@ -125,7 +125,7 @@ export class RustlikeResult<T, E> implements Result<T, E> {
      *
      * ref: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_err
      */
-    isErr(): boolean {
+    isErr(): this is Result<never, E> {
         return this._type === 'err';
     }
 

diff --git a/src/types.ts b/src/types.ts
@@ -28,7 +28,7 @@ export interface Result<T, E> {
      *
      * ref: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_ok
      */
-    isOk(): boolean;
+    isOk(): this is Result<T, never>;
 
     /**
      * Returns `true` if the result is `Ok` and the value inside of it matches a predicate.
@@ -91,7 +91,7 @@ export interface Result<T, E> {
      *
      * ref: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_err
      */
-    isErr(): boolean;
+    isErr(): this is Result<never, E>;
 
     /**
      * Returns `true` if the result is `Err` and the value inside of it matches a predicate.