`T extends U ? X : Y` lets types branch on shape. Combine with `infer` to extract pieces of complex types — the building block under `ReturnType`, `Parameters`, and most utility libraries.
TypeScript
// Extract the resolved value of a Promise (or leave non-promise types alone).
type Unwrap<T> = T extends Promise<infer U> ? U : T;
type A = Unwrap<Promise<string>>; // string
type B = Unwrap<number>; // number
// Extract function argument types as a tuple.
type Args<F> = F extends (...args: infer P) => any ? P : never;
type FirstArg<F> = Args<F>[0];
const greet = (name: string, formal: boolean) => `Hello, ${name}`;
type Greeting = ReturnType<typeof greet>; // string
type GreetArgs = Args<typeof greet>; // [string, boolean]
type WhosName = FirstArg<typeof greet>; // stringSave your own code snippets
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