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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,203 @@ | ||
| /** | ||
| * A generic Result class that represents either a success value or an error. | ||
| * This class is useful for handling operations that can fail, providing a type-safe | ||
| * way to represent and handle both successful and failed outcomes. | ||
| * | ||
| * @typeparam T The type of the success value. | ||
| */ | ||
| // TODO: add an idea of asyncResult where | ||
| // we have "unasked", error, success to more accurately | ||
| // represent that data isnt "null", we just | ||
| // haven't tried to get it yet | ||
| export class Result<T> { | ||
| private constructor( | ||
| private readonly value: T | null, | ||
| private readonly error: Error | null | ||
| ) {} | ||
|
|
||
| /** | ||
| * Creates a successful Result containing the given value. | ||
| * | ||
| * @param value The value to be wrapped in a successful Result. | ||
| * @returns A new Result instance representing a success. | ||
| * | ||
| * @example | ||
| * const successResult = Result.success(42); | ||
| * console.log(successResult.isSuccess()); // true | ||
| * console.log(successResult.getValue()); // 42 | ||
| */ | ||
| static success<U>(value: U): Result<U> { | ||
| return new Result(value, null); | ||
| } | ||
|
|
||
| /** | ||
| * Creates a failed Result containing the given error. | ||
| * | ||
| * @param error The error to be wrapped in a failed Result. | ||
| * @returns A new Result instance representing a failure. | ||
| * | ||
| * @example | ||
| * const failureResult = Result.failure(new Error("Something went wrong")); | ||
| * console.log(failureResult.isFailure()); // true | ||
| * console.log(failureResult.getError().message); // "Something went wrong" | ||
| */ | ||
| static failure<U>(error: Error): Result<U> { | ||
| return new Result<U>(null, error); | ||
| } | ||
|
|
||
| /** | ||
| * Checks if the Result is successful. | ||
| * | ||
| * @returns true if the Result represents a success, false otherwise. | ||
| * | ||
| * @example | ||
| * const result = Result.success("Hello"); | ||
| * console.log(result.isSuccess()); // true | ||
| */ | ||
| isSuccess(): boolean { | ||
| return this.error === null; | ||
| } | ||
|
|
||
| /** | ||
| * Checks if the Result is a failure. | ||
| * | ||
| * @returns true if the Result represents a failure, false otherwise. | ||
| * | ||
| * @example | ||
| * const result = Result.failure(new Error("Oops")); | ||
| * console.log(result.isFailure()); // true | ||
| */ | ||
| isFailure(): boolean { | ||
| return this.error !== null; | ||
| } | ||
|
|
||
| /** | ||
| * Gets the success value if the Result is successful. | ||
| * | ||
| * @returns The success value. | ||
| * @throws Error if the Result represents a failure. | ||
| * | ||
| * @example | ||
| * const result = Result.success("Hello, World!"); | ||
| * if (result.isSuccess()) { | ||
| * console.log(result.getValue()); // "Hello, World!" | ||
| * } | ||
| */ | ||
| getValue(): T { | ||
| if (this.isFailure()) { | ||
| throw new Error("Cannot get value from a failed Result"); | ||
| } | ||
| return this.value as T; | ||
| } | ||
|
|
||
| /** | ||
| * Gets the error if the Result is a failure. | ||
| * | ||
| * @returns The error. | ||
| * @throws Error if the Result represents a success. | ||
| * | ||
| * @example | ||
| * const result = Result.failure(new Error("File not found")); | ||
| * if (result.isFailure()) { | ||
| * console.log(result.getError().message); // "File not found" | ||
| * } | ||
| */ | ||
| getError(): Error { | ||
| if (this.isSuccess()) { | ||
| throw new Error("Cannot get error from a successful Result"); | ||
| } | ||
| return this.error as Error; | ||
| } | ||
|
|
||
| /** | ||
| * Applies a function to the contained value if the Result is a success. | ||
| * If the Result is a failure, it returns a new Result with the same error. | ||
| * Use map when your transformation always succeeds and returns a regular value. | ||
| * | ||
| * @param fn The function to apply to the success value. | ||
| * @returns A new Result containing the result of the function application, or the original error. | ||
| * | ||
| * @example | ||
| * // Success case | ||
| * const successResult = Result.success(5); | ||
| * const doubled = successResult.map(x => x * 2); | ||
| * console.log(doubled.getValue()); // 10 | ||
| * | ||
| * // Failure case | ||
| * const failureResult = Result.failure<number>(new Error("Invalid input")); | ||
| * const shouldNotDouble = failureResult.map(x => x * 2); | ||
| * console.log(shouldNotDouble.isFailure()); // true | ||
| * console.log(shouldNotDouble.getError().message); // "Invalid input" | ||
| */ | ||
| map<U>(fn: (value: T) => U): Result<U> { | ||
| if (this.isSuccess()) { | ||
| return Result.success(fn(this.getValue())); | ||
| } | ||
| return Result.failure(this.getError()); | ||
| } | ||
|
|
||
| /** | ||
| * Applies a function that returns a Result to the contained value if this Result is a success. | ||
| * If this Result is a failure, it returns a new Result with the same error. | ||
| * Use flatMap when your transformation might fail or when it returns another Result. | ||
| * | ||
| * The key difference between map and flatMap: | ||
| * - map is for simple transformations that always succeed. | ||
| * - flatMap is for operations that might fail or that return a Result themselves. | ||
| * | ||
| * @param fn The function to apply to the success value. | ||
| * @returns The Result returned by the function, or this Result if it's a failure. | ||
| * | ||
| * @example | ||
| * function divide(a: number, b: number): Result<number> { | ||
| * if (b === 0) return Result.failure(new Error("Division by zero")); | ||
| * return Result.success(a / b); | ||
| * } | ||
| * | ||
| * // Success case | ||
| * const successResult = Result.success(10) | ||
| * .flatMap(x => divide(x, 2)) | ||
| * .flatMap(x => divide(x, 2)); | ||
| * console.log(successResult.getValue()); // 2.5 | ||
| * | ||
| * // Failure case: division by zero | ||
| * const failureResult = Result.success(10) | ||
| * .flatMap(x => divide(x, 2)) | ||
| * .flatMap(x => divide(x, 0)); | ||
| * console.log(failureResult.isFailure()); // true | ||
| * console.log(failureResult.getError().message); // "Division by zero" | ||
| * | ||
| * // Failure case: starting with a failure | ||
| * const initialFailure = Result.failure<number>(new Error("Initial error")) | ||
| * .flatMap(x => divide(x, 2)); | ||
| * console.log(initialFailure.isFailure()); // true | ||
| * console.log(initialFailure.getError().message); // "Initial error" | ||
| * | ||
| * // Example demonstrating the need for flatMap: | ||
| * function getUser(id: number): Result<User> { | ||
| * // Imagine this fetches a user from a database | ||
| * // It might fail, so it returns a Result | ||
| * } | ||
| * | ||
| * function getUserEmail(user: User): Result<string> { | ||
| * // This might fail if the user doesn't have an email | ||
| * // So it also returns a Result | ||
| * } | ||
| * | ||
| * // Using flatMap to chain operations that return Results | ||
| * const userEmailResult = getUser(123) | ||
| * .flatMap(user => getUserEmail(user)); | ||
| * | ||
| * // If we tried to use map, it wouldn't work correctly: | ||
| * const incorrectResult = getUser(123) | ||
| * .map(user => getUserEmail(user)); // This would be Result<Result<string>>, not what we want! | ||
| * | ||
| * // flatMap "flattens" the nested Result, giving us a Result<string> as desired. | ||
| */ | ||
| flatMap<U>(fn: (value: T) => Result<U>): Result<U> { | ||
| if (this.isSuccess()) { | ||
| return fn(this.getValue()); | ||
| } | ||
| return Result.failure(this.getError()); | ||
| } | ||
| } |
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