byethrow
  • English

      • no-negated-type-guards

      Disallows using the negation operator (!) on Result.isSuccess() or Result.isFailure().

      Rule details

      !Result.isSuccess(result) is equivalent to Result.isFailure(result), but the negated form is less readable and requires an extra mental step to parse. This rule auto-fixes violations.

      Incorrect

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<string, Error>
      result      : 
      import Result
      Result      .
      type Result<T, E> = Result.Success<T> | Result.Failure<E>
      A union type representing either a success or a failure.
      @typeParamT  - The type of the Success value.@typeParamE  - The type of the Failure value.@example
      import { Result } from '@praha/byethrow';

const doSomething = (): Result.Result<number, string> => {
  return Math.random() > 0.5
    ? { type: 'Success', value: 10 }
    : { type: 'Failure', error: 'Oops' };
};
      @categoryCore  Types
      Result      <string, Error> = 
      import Result
      Result      .
      const succeed: <"hello">(value: "hello") => Result.Result<"hello", never> (+1 overload)
      succeed      ('hello');      

// ❌ negating isSuccess
if (!
      import Result
      Result      .
      const isSuccess: <Result.Result<string, Error>>(result: Result.Result<string, Error>) => result is Result.Success<string>
      Type guard to check if a
Result
is a
Success 
.
      @function@typeParamR  - The type of the result to check.@paramresult  - The Result to check.@returnstrue if the result is a Success , otherwise false.@example
      import { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Success', value: 10 };
if (Result.isSuccess(result)) {
  console.log(result.value); // Safe access to value
}
      @categoryType  Guards
      isSuccess      (
      const result: Result.Result<string, Error>
      result      )) {      
  // handle failure
}

// ❌ negating isFailure
if (!
      import Result
      Result      .
      const isFailure: <Result.Result<string, Error>>(result: Result.Result<string, Error>) => result is Result.Failure<Error>
      Type guard to check if a
Result
is a
Failure 
.
      @function@typeParamR  - The type of the result to check.@paramresult  - The Result to check.@returnstrue if the result is a Failure , otherwise false.@example
      import { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Failure', error: 'Something went wrong' };
if (Result.isFailure(result)) {
  console.error(result.error); // Safe access to error
}
      @categoryType  Guards
      isFailure      (
      const result: Result.Result<string, Error>
      result      )) {      
  // handle success
}

      Correct

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<string, Error>
      result      : 
      import Result
      Result      .
      type Result<T, E> = Result.Success<T> | Result.Failure<E>
      A union type representing either a success or a failure.
      @typeParamT  - The type of the Success value.@typeParamE  - The type of the Failure value.@example
      import { Result } from '@praha/byethrow';

const doSomething = (): Result.Result<number, string> => {
  return Math.random() > 0.5
    ? { type: 'Success', value: 10 }
    : { type: 'Failure', error: 'Oops' };
};
      @categoryCore  Types
      Result      <string, Error> = 
      import Result
      Result      .
      const succeed: <"hello">(value: "hello") => Result.Result<"hello", never> (+1 overload)
      succeed      ('hello');      

// ✅ using the direct type guard
if (
      import Result
      Result      .
      const isFailure: <Result.Result<string, Error>>(result: Result.Result<string, Error>) => result is Result.Failure<Error>
      Type guard to check if a
Result
is a
Failure 
.
      @function@typeParamR  - The type of the result to check.@paramresult  - The Result to check.@returnstrue if the result is a Failure , otherwise false.@example
      import { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Failure', error: 'Something went wrong' };
if (Result.isFailure(result)) {
  console.error(result.error); // Safe access to error
}
      @categoryType  Guards
      isFailure      (
      const result: Result.Result<string, Error>
      result      )) {      
  // handle failure
}

if (
      import Result
      Result      .
      const isSuccess: <Result.Result<string, Error>>(result: Result.Result<string, Error>) => result is Result.Success<string>
      Type guard to check if a
Result
is a
Success 
.
      @function@typeParamR  - The type of the result to check.@paramresult  - The Result to check.@returnstrue if the result is a Success , otherwise false.@example
      import { Result } from '@praha/byethrow';

const result: Result.Result<number, string> = { type: 'Success', value: 10 };
if (Result.isSuccess(result)) {
  console.log(result.value); // Safe access to value
}
      @categoryType  Guards
      isSuccess      (
      const result: Result.Result<string, Error>
      result      )) {      
  // handle success
}