If

Bring conditional logic to TypeScript's type system! 🤔

In this easy-level challenge, you'll implement a utility type If<C, T, F> that works like a ternary operator at the type level. Based on a boolean condition C, it returns either the truthy type T or the falsy type F. This is a fundamental building block for creating dynamic, conditional types.

You'll learn how conditional types work with boolean literals and how TypeScript's type system handles boolean union types, providing insights into type-level branching logic.

For this challenge, you will need to change the following code to make the tests pass (no type check errors).

type A = If<true, 'a', 'b'>  // expected to be 'a'
type B = If<false, 'a', 'b'> // expected to be 'b'

Detailed Explanation

The If utility type uses TypeScript's conditional types to implement branching logic.

type If<C extends boolean, T, F> = C extends true ? T : F

Key insights:

• C extends boolean constrains C to boolean values
• When C is exactly true, return T
• When C is exactly false, return F
• When C is boolean (union of true | false), the conditional distributes, returning T | F

This simple pattern enables powerful type-level conditionals and is used extensively in complex type utilities to make decisions based on type information.