व्यवहार में T extends U ? X : Y

type IsString<T> = T extends string ? true : false

type A = IsString<string>
//   ^ true

type B = IsString<number>
//   ^ false

type ToArray<T> = T extends any ? T[] : never

type C = ToArray<string | number>
// distributes:
// C is string[] | number[]

type ToArrayNoDist<T> = [T] extends [any] ? T[] : never

type D = ToArrayNoDist<string | number>
// no distribution:
// D is (string | number)[]

type NonEmptyArray<T> = T[] extends [] ? never : T[]
// Usually better:
// type ElementType<T> = T extends ReadonlyArray<infer U> ? U : T

type E1 = ElementType<string[]>
//   ^ string

type E2 = ElementType<readonly number[]>
//   ^ number

type E3 = ElementType<string>
//   ^ string

// Tips
// - Keep conditions simple; deep nesting harms readability
// - Document distribution behavior for teammates
// - Prefer helper aliases (ElementType, Awaited) for reuse
// - Watch for De Morgan like logic when composing unions