Numerous varieties of return types

Question

Numerous varieties of return types

Is it meant by this

function foo(): () => void | string

that

a) the function foo might return a string, or another function that doesn't return anything; or

b) the function foo returns a different function, which may or may not return a string?

Furthermore, how can you accurately and distinctly represent the alternative option (the incorrect one)?

typescript

Answer 1

Answer №1

function bar(): () => void | string

: bar is a function with no parameters that will output either void or string

function baz(): void | string : baz is a function without input params and will return either void or string

function qux(): (() => void) | string

: qux is a function that takes no inputs and returns either string or another function that yields void

Answer 2

function bar(): () => void | string

: bar is a function with no parameters that will output either void or string

function baz(): void | string : baz is a function without input params and will return either void or string

function qux(): (() => void) | string

: qux is a function that takes no inputs and returns either string or another function that yields void

Answer 3

Answer №2

() => void | string represents a function type that may or may not return a string. However, this seems redundant because a function returning a string can already be assigned to () => void.

If you intend to specify "either a function or a string", you should use parentheses like this: (() => void) | string. This is similar to using parentheses in any other situation where the order of operations needs to be clarified.

Answer 4

() => void | string represents a function type that may or may not return a string. However, this seems redundant because a function returning a string can already be assigned to () => void.

If you intend to specify "either a function or a string", you should use parentheses like this: (() => void) | string. This is similar to using parentheses in any other situation where the order of operations needs to be clarified.

Answer 5

Answer №3

Explanation of option (b)

/**
 * The function foo takes no arguments and returns another function,
 * which may or may not return a string.
 */
function foo(): () => void | string;

// example implementation
function foo(): () => void | string {
  return () => {
    if (Math.random() % 2 === 0) {
      return "bar";
    }
  };
}

Definition of option (a)

/**
 * The function foo2 can return either a string,
 * or another function that does not return anything.
 */
function foo2(): (() => void) | string;

// example implementation
function foo2(): (() => void) | string {
  if (Math.random() % 2 === 0) { 
    return "bar"; 
  }

  return () => {};
}

Answer 6

Explanation of option (b)

/**
 * The function foo takes no arguments and returns another function,
 * which may or may not return a string.
 */
function foo(): () => void | string;

// example implementation
function foo(): () => void | string {
  return () => {
    if (Math.random() % 2 === 0) {
      return "bar";
    }
  };
}

Definition of option (a)

/**
 * The function foo2 can return either a string,
 * or another function that does not return anything.
 */
function foo2(): (() => void) | string;

// example implementation
function foo2(): (() => void) | string {
  if (Math.random() % 2 === 0) { 
    return "bar"; 
  }

  return () => {};
}

Numerous varieties of return types

Answer №1

Answer №2

Answer №3

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