TypeScript Discriminated Unions with Template String types

retool-typescript-control-flow-analysis-12.ts

interface Success {
  type: `${string}Success`;
  body: string;
}

interface Error {
  type: `${string}Error`;
  message: string;
}

function handler(r: Success | Error) {
  if (r.type === "HttpSuccess") {
    r
    // `r` is of type `Success`
  } else if (r.type === "NetworkError") {
    r
    // `r` is of type `Error`
  } else if (r.type === "ServerError") {
    r
    // `r` is of type `Error`
  }
}