โ Based in Sao Paulo, Brazil
ฯ Currently building type-safe systems
Exhaustiveness checking in TypeScript
Home Page: https://www.npmjs.com/package/exhaustive
License: MIT License
I noticed in the example below, the first function is detected by TypeScript as being type unsafe but the second is not. Any ideas why?
import { exhaustive } from "exhaustive";
export type Copyable =
| { type: "text"; text: string }
| { type: "file"; file: File }
| { type: "url"; url: string; contentType: string };
export type Input = { type: "text"; value: string };
// No Typescript Error
const copyableNotTypeSafe = async (input: Input): Promise<Copyable | null> => {
return await exhaustive.tag(input, "type", {
text: async () => {
return {
type: "text",
fieldDNE: "FIELD DOES NOT EXISTS"
};
},
_: async () => null
});
};
// Typescript correctly detects result is the wrong type
const copyableTypeSafe = async (input: Input): Promise<Copyable | null> => {
const result = await exhaustive.tag(input, "type", {
text: async () => {
return {
type: "text",
fieldDNE: "FIELD DOES NOT EXISTS"
};
},
_: async () => null
});
return result;
};
Sandbox demo with typescript errors: https://codesandbox.io/s/typescript-playground-export-forked-m27tfl?file=/index.ts
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