customized-fields.ts

customized-fields.ts

// custom type names
type CustomType = "type1" | "type2";

// mapping from custom type names to TypeScript types
type TypeOf<T extends CustomType> =
	T extends "type1" ? string
	: T extends "type2" ? number
	: never;

// generic Options type parametrized by custom types
type Options<T extends CustomType> = {
	type: T;
	value: TypeOf<T>;
}

// field names associated with custom type names
type Fields = {
	[k: string]: CustomType
}

// field configuration as keys associated with Options
type Configuration<F extends Fields> = {
	[P in keyof F]: F[P] extends CustomType ? Options<F[P]> : never;
}

// Result with keys typed by configuration 
type Result<F extends Fields> = {
	[P in keyof F]: F[P] extends infer T extends CustomType ? TypeOf<T> : never;
}

// function parametrized by configuration returning typed result
function foo<F extends Fields>(f: Configuration<F>) {
	return {} as Result<F>;
}

// example
const test = foo({
	field_a: {
		type: "type1",

		// type "string" is determined by "type1" name
		value: "test string"
	},
	field_b: {
		type: "type2",

		// type "number" is determined by "type2" name
		value: 10
	}
})

// we have functional intellisense for the entire configuration as
// well as for the result  

// type "string"
const fa_val = test.field_a;

// type "number"
const fb_val = test.field_b;

export { test };