Discriminated Unions

Discriminated unions use a common field to decide type. ## Example: API state ```ts type Loading = { status: "loading" }; type Success = { status: "success"; data: string }; type ErrorState = { status: "error"; message: string }; type State = Loading | Success | ErrorState; ``` ## Handle safely ```ts function render(s: State) { switch (s.status) { case "loading": return "Loading..."; case "success": return s.data; case "error": return s.message; } } ``` TypeScript knows which fields exist. ## Graph ```mermaid flowchart TD A[State] --> B[loading] A --> C[success] A --> D[error] ``` ## Remember - Use a shared tag field - Makes logic safe and readable