Discriminated Unions

A discriminated union is a union of object types that share one literal property, the tag, such as kind: "circle" or kind: "square". Checking the tag narrows to exactly one member, so each branch knows which properties exist. Add a never check in the default branch and TypeScript will flag any member you forget to handle.

How it reads

• kind is the tag every member shares
• Inside case "circle", only radius is available
• Assigning to never fails to compile if a case was missed

Cloud tip: Tagged unions are the TypeScript way to model states: loading, success, error. Each state carries only the data that makes sense for it.