universal-overloading.ts

const libs = []

export enum Types {
    number,
    numbers,
    string,
    buffer,
}

export enum Actions {
    add,
    subtract,
    readFile,
}

libs.push({
	action: Actions.add,
	from: Types.numbers,
	get: Types.number,
	fn: (...n: number[]): number => n.reduce((a, b) => a + b, 0),
})

libs.push({
	action: Actions.subtract,
	from: Types.numbers,
	get: Types.number,
	fn: (...n: number[]): number => n.reduce((a, b) => a - b, 0),
})

libs.push({
	action: Actions.readFile,
	from: Types.string,
	get: Types.string,
	fn: async (s:string): Promise<string> => promisify(fs.readFile)(s, 'UTF8'),
})

libs.push({
	action: Actions.readFile,
	from: Types.string,
	get: Types.buffer,
	fn: async (s:string): Promise<Buffer> => promisify(fs.readFile)(s),
})

const library = (a: Actions, from: Types, get: Types, lib) => {
    const found = lodash.find(lib, fn => {
        return (
        lodash.isEqual(fn.from, from) &&
        lodash.isEqual(fn.get, get)
        );
    });
    if (!found) throw new Error('no conversion');
    return found.fn;
}

const { readFile } = Actions;
const { string: s } = Types;

const x = library(readFile, s, s, libs)

x('./tres.ts').then(console.log)