Function err

Create an instance of Err.

If you need to create an instance with a specific type (as you do whenever you are not constructing immediately for a function return or as an argument to a function), you can use a type parameter:

const notString = Result.err<number, string>('something went wrong');
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Note: passing nothing, or passing null or undefined explicitly, will produce a Result<T, Unit>, rather than producing the nonsensical and in practice quite annoying Result<null, string> etc. See Unit for more.

const normalResult = Result.err<number, string>('oh no');
const explicitUnit = Result.err<number, Unit>(Unit);
const implicitUnit = Result.err<number, Unit>();
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In the context of an immediate function return, or an arrow function with a single expression value, you do not have to specify the types, so this can be quite convenient.

type SomeData = {
  //...
};

const isValid = (data: SomeData): boolean => {
  // true or false...
}

const arrowValidate = (data: SomeData): Result<number, Unit> =>
  isValid(data) ? Result.ok(42) : Result.err();

function fnValidate(data: someData): Result<number, Unit> {
  return isValid(data) ? Result.ok(42) : Result.err();
}
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