access specific key of interface with parameter of function-CodePudding

basically speaking i have two interfaces:


interface config {
    lang: "en" | "de";
    test: number;
}

interface Accessor {
    key ( k: keyof config ): config[k];
}

and i want to dynamically have the type of whatever i access from the config type, via the Accessor object. is that possible?

note: my code is a lot more complicated and i cannot just access the keys directly, but it boils down to this in the end

CodePudding user response：

The key() method signature in your Accessor interface should return an indexed access type of the form Config[X] where X is the type of the k parameter. Your attempt, Config[k], is not valid, because k is the value of the parameter; you need its type. This can be remedied using the typeof type operator like so:

interface Accessor {
    key(k: keyof Config): Config[typeof k];
}

This now compiles with no error. And you can even use it:

declare const a: Accessor;
const langProp = a.key("lang");
// const langProp: number | "en" | "de"