ArgsType.ts

argsType.ts

type ArgsType<T> = T extends (...args: infer R) => any ? R : never;

type Func1 = (a: string, b: boolean) => boolean;
type Func2 = () => void;

const pass1: ArgsType<Func1> = ["yay", true];
const fail1: ArgsType<Func1> = ["yay"];
const fail2: ArgsType<Func1> = [true, true];
const fail3: ArgsType<Func1> = [];
const fail4: ArgsType<Func1> = ["yay", true, "boo"];

const pass2: ArgsType<Func2> = [];
const fail5: ArgsType<Func2> = "boo";
const fail6: ArgsType<Func2> = "";
const fail7: ArgsType<Func2> = [null];
const fail8: ArgsType<Func2> = null; // false pass, but ignorable

type Func3<R> = (f: (...T) => any) => ((...T) => R);
const f1 = (a: string, b: boolean):string => { return ''; };
const f2 = (): any[] => ["yay"];

const fluent = ((f) => (...args) => {
	f(...args);
	return {fluent: true};
}) as Func3<{fluent: true}>; // I have no idea how to construct this

const pass3: {fluent: true} = fluent(f1)("yay", true);
const fail9: {fluent: true} = fluent(f1)("yay"); // TODO: FALSE PASS
const fail10: {fluent: true} = fluent(f1)("yay", "boo"); // TODO: FALSE PASS