Add this context support to safeTry function

README.md

@@ -1582,7 +1582,7 @@ declare function mayFail1(): Result<number, string>;
 declare function mayFail2(): Result<number, string>;
 
 function myFunc(): Result<number, string> {
-    return safeTry<number, string>(function*() {
+    return safeTry(function*() {
         return ok(
             // If the result of mayFail1().mapErr() is an `Err`, the evaluation is
             // aborted here and the enclosing `safeTry` block is evaluated to that `Err`.
@@ -1603,14 +1603,15 @@ To use `safeTry`, the points are as follows.
 * In that block, you can use `yield* <RESULT>` to state 'Return `<RESULT>` if it's an `Err`, otherwise evaluate to its `.value`'
 * Pass the generator function to `safeTry`
 
-You can also use [async generator function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function*) to pass an async block to `safeTry`.
+You can also use [async generator function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function*) to pass an async block to `safeTry`. For more information, see https://github.com/supermacro/neverthrow/pull/448 and https://github.com/supermacro/neverthrow/issues/444
+
 ```typescript
 // You can use either Promise<Result> or ResultAsync.
 declare function mayFail1(): Promise<Result<number, string>>;
 declare function mayFail2(): ResultAsync<number, string>;
 
-function myFunc(): Promise<Result<number, string>> {
-    return safeTry<number, string>(async function*() {
+function myFunc(): ResultAsync<number, string> {
+    return safeTry(async function*() {
         return ok(
             // You have to await if the expression is Promise<Result>
             (yield* (await mayFail1())
@@ -1624,7 +1625,26 @@ function myFunc(): Promise<Result<number, string>> {
 }
 ```
 
-For more information, see https://github.com/supermacro/neverthrow/pull/448 and https://github.com/supermacro/neverthrow/issues/444
+Additionally, when using `safeTry` in class methods, you can pass `this` context as the first argument:
+
+```typescript
+class MyClass {
+  mayFail1: () => Promise<Result<number, string>>;
+  mayFail2: () => ResultAsync<number, string>;
+
+  myFunc(): ResultAsync<number, string> {
+    return safeTry(this, async function*() {
+        return ok(
+            (yield* (await this.mayFail1())
+                .mapErr(e => `aborted by an error from 1st function, ${e}`))
+            +
+            (yield* this.mayFail2()
+                .mapErr(e => `aborted by an error from 2nd function, ${e}`))
+        )
+    })
+  }
+}
+```
 
 [⬆️  Back to top](#toc)
 

src/result.ts

@@ -86,6 +86,23 @@ export function err<T = never, E = unknown>(err: E): Err<T, E> {
  * @returns The first occurrence of either an yielded Err or a returned Result.
  */
 export function safeTry<T, E>(body: () => Generator<Err<never, E>, Result<T, E>>): Result<T, E>
+
+/**
+ * Evaluates the given generator to a Result returned or an Err yielded from it,
+ * whichever comes first.
+ *
+ * This function is intended to emulate Rust's ? operator.
+ * See `/tests/safeTry.test.ts` for examples.
+ *
+ * @param thisArg - The `this` context to bind to the generator function
+ * @param body - What is evaluated. In body, `yield* result` works as
+ * Rust's `result?` expression.
+ * @returns The first occurrence of either an yielded Err or a returned Result.
+ */
+export function safeTry<T, E, This>(
+  thisArg: This,
+  body: (this: This) => Generator<Err<never, E>, Result<T, E>>,
+): Result<T, E>
 export function safeTry<
   YieldErr extends Err<never, unknown>,
   GeneratorReturnResult extends Result<unknown, unknown>
@@ -96,6 +113,30 @@ export function safeTry<
   InferErrTypes<YieldErr> | InferErrTypes<GeneratorReturnResult>
 >
 
+/**
+ * Evaluates the given generator to a Result returned or an Err yielded from it,
+ * whichever comes first.
+ *
+ * This function is intended to emulate Rust's ? operator.
+ * See `/tests/safeTry.test.ts` for examples.
+ *
+ * @param thisArg - The `this` context to bind to the generator function
+ * @param body - What is evaluated. In body, `yield* result` works as
+ * Rust's `result?` expression.
+ * @returns The first occurrence of either an yielded Err or a returned Result.
+ */
+export function safeTry<
+  YieldErr extends Err<never, unknown>,
+  GeneratorReturnResult extends Result<unknown, unknown>,
+  This
+>(
+  thisArg: This,
+  body: (this: This) => Generator<YieldErr, GeneratorReturnResult>,
+): Result<
+  InferOkTypes<GeneratorReturnResult>,
+  InferErrTypes<YieldErr> | InferErrTypes<GeneratorReturnResult>
+>
+
 /**
  * Evaluates the given generator to a Result returned or an Err yielded from it,
  * whichever comes first.
@@ -110,6 +151,24 @@ export function safeTry<
 export function safeTry<T, E>(
   body: () => AsyncGenerator<Err<never, E>, Result<T, E>>,
 ): ResultAsync<T, E>
+
+/**
+ * Evaluates the given generator to a Result returned or an Err yielded from it,
+ * whichever comes first.
+ *
+ * This function is intended to emulate Rust's ? operator.
+ * See `/tests/safeTry.test.ts` for examples.
+ *
+ * @param thisArg - The `this` context to bind to the generator function
+ * @param body - What is evaluated. In body, `yield* result` and
+ * `yield* resultAsync` work as Rust's `result?` expression.
+ * @returns The first occurrence of either an yielded Err or a returned Result.
+ */
+export function safeTry<T, E, This>(
+  thisArg: This,
+  body: (this: This) => AsyncGenerator<Err<never, E>, Result<T, E>>,
+): ResultAsync<T, E>
+
 export function safeTry<
   YieldErr extends Err<never, unknown>,
   GeneratorReturnResult extends Result<unknown, unknown>
@@ -119,18 +178,51 @@ export function safeTry<
   InferOkTypes<GeneratorReturnResult>,
   InferErrTypes<YieldErr> | InferErrTypes<GeneratorReturnResult>
 >
-export function safeTry<T, E>(
-  body:
-    | (() => Generator<Err<never, E>, Result<T, E>>)
-    | (() => AsyncGenerator<Err<never, E>, Result<T, E>>),
+
+/**
+ * Evaluates the given generator to a Result returned or an Err yielded from it,
+ * whichever comes first.
+ *
+ * This function is intended to emulate Rust's ? operator.
+ * See `/tests/safeTry.test.ts` for examples.
+ *
+ * @param thisArg - The `this` context to bind to the generator function
+ * @param body - What is evaluated. In body, `yield* result` and
+ * `yield* resultAsync` work as Rust's `result?` expression.
+ * @returns The first occurrence of either an yielded Err or a returned Result.
+ */
+export function safeTry<
+  YieldErr extends Err<never, unknown>,
+  GeneratorReturnResult extends Result<unknown, unknown>,
+  This
+>(
+  thisArg: This,
+  body: (this: This) => AsyncGenerator<YieldErr, GeneratorReturnResult>,
+): ResultAsync<
+  InferOkTypes<GeneratorReturnResult>,
+  InferErrTypes<YieldErr> | InferErrTypes<GeneratorReturnResult>
+>
+
+export function safeTry<T, E, This>(
+  bodyOrThisArg: (() => ResultReturnGenerator<T, E>) | This,
+  body?: (this: This) => ResultReturnGenerator<T, E>,
 ): Result<T, E> | ResultAsync<T, E> {
-  const n = body().next()
+  const g =
+    body == undefined
+      ? (bodyOrThisArg as () => ResultReturnGenerator<T, E>)()
+      : (body.call(bodyOrThisArg) as ResultReturnGenerator<T, E>)
+  const n = g.next()
+
   if (n instanceof Promise) {
     return new ResultAsync(n.then((r) => r.value))
   }
   return n.value
 }
 
+type ResultReturnGenerator<T, E> =
+  | Generator<Err<never, E>, Result<T, E>>
+  | AsyncGenerator<Err<never, E>, Result<T, E>>
+
 interface IResult<T, E> {
   /**
    * Used to check if a `Result` is an `OK`

tests/safe-try.test.ts

@@ -23,6 +23,14 @@ describe('Returns what is returned from the generator function', () => {
     expect(res._unsafeUnwrap()).toBe(val)
   })
 
+  test("With synchronous Ok and this context", () => {
+    const res = safeTry(val, function*() {
+      return ok(this)
+    })
+    expect(res).toBeInstanceOf(Ok)
+    expect(res._unsafeUnwrap()).toBe(val)
+  })
+
   test("With synchronous Err", () => {
     const res = safeTry(function*() {
       return err(val)
@@ -31,6 +39,14 @@ describe('Returns what is returned from the generator function', () => {
     expect(res._unsafeUnwrapErr()).toBe(val)
   })
 
+  test("With synchronous Err and this context", () => {
+    const res = safeTry(val, function*() {
+      return err(this)
+    })
+    expect(res).toBeInstanceOf(Err)
+    expect(res._unsafeUnwrapErr()).toBe(val)
+  })
+
   test("With async Ok", async () => {
     const res = await safeTry(async function*() {
       return await okAsync(val)
@@ -39,13 +55,29 @@ describe('Returns what is returned from the generator function', () => {
     expect(res._unsafeUnwrap()).toBe(val)
   })
 
+  test("With async Ok and this context", async () => {
+    const res = await safeTry(val, async function*() {
+      return await okAsync(this)
+    })
+    expect(res).toBeInstanceOf(Ok)
+    expect(res._unsafeUnwrap()).toBe(val)
+  })
+
   test("With async Err", async () => {
     const res = await safeTry(async function*() {
       return await errAsync(val)
     })
     expect(res).toBeInstanceOf(Err)
     expect(res._unsafeUnwrapErr()).toBe(val)
   })
+
+  test("With async Err and this context", async () => {
+    const res = await safeTry(val, async function*() {
+      return await errAsync(this)
+    })
+    expect(res).toBeInstanceOf(Err)
+    expect(res._unsafeUnwrapErr()).toBe(val)
+  })
 })
 
 describe("Returns the first occurence of Err instance as yiled*'s operand", () => {