110 tokens

Narrowing

Type narrowing as usual.

Narrowing

type narrowing as usual, narrowing is just doing runtime type checking
instanceof, typeof, is
typeof in type position
is for type queries
instanceof for classes
match narrowing

src/narrowing.ds.ds

1type Event =2    | { kind: "ready"; port: uint16 }3    | { kind: "closed"; reason: string };4 5function describe(event: Event): string {6    if (event.kind == "ready") {7        return `listening on ${event.port}`;8    }9 10    event.reason11}