Theo's Typesafe Cult•2y ago

TypeScript Mapped Types

Hey. I have this type which uses mapped types to generate this other type. It works a little bit, but I'd like it to generate a different type of type union.

1 Reply

domi?•2y ago

const functions = [
    {
        type: 'on',
        path: 'test1',
        callback: (_: Electron.IpcMainEvent, __: number) => 0
    },
    {
        type: 'on',
        path: 'test2',
        callback: (_: Electron.IpcMainEvent, __: string) => '0'
    }
] as const;


type Renderer<Functions extends IPCFunction> = {
    [Fn in Functions as 'send']: (channel: Fn['path'], ...args: Parameters<Fn['callback']>) => void;
};

type RouterType = typeof functions;

let renderer: Renderer<RouterType[number]>;

renderer.send();

const functions = [
    {
        type: 'on',
        path: 'test1',
        callback: (_: Electron.IpcMainEvent, __: number) => 0
    },
    {
        type: 'on',
        path: 'test2',
        callback: (_: Electron.IpcMainEvent, __: string) => '0'
    }
] as const;


type Renderer<Functions extends IPCFunction> = {
    [Fn in Functions as 'send']: (channel: Fn['path'], ...args: Parameters<Fn['callback']>) => void;
};

type RouterType = typeof functions;

let renderer: Renderer<RouterType[number]>;

renderer.send();

The type of renderer.send is

(channel: "test2" | "test1", ...args: [_: Electron.IpcMainEvent, __: number] | [_: Electron.IpcMainEvent, __: string]) => void

. It's nice but it could be improved. Is there any way to make it

((channel: "test1", ...args: [_: Electron.IpcMainEvent, __: number]) => void) | ((channel: "test2", ...args: [_: Electron.IpcMainEvent, __: string]) => void)

? I ended up mapping the types into an object first, then just grab each of its values and putting it into a union and it worked fine 👍

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TypeScript Mapped Types