type A = {
	type: "atype";
	acontent: string;
}

type B = {
	type: "btype";
	bcontent: string
}

function fn1(val: A|B) {
	if(val.type === "atype") {
		console.log(val.acontent);
	}
	if(val.type === "btype") {
		console.log(val.bcontent);
	}
}

type Modified<T extends A|B> =
	Omit<T, "type"> & {
		type: `prefix-${T["type"]}`;
	};

function fn2(val: Modified<A|B>) {
	if(val.type === "prefix-atype") {
		console.log(val.acontent);
	}
	if(val.type === "prefix-btype") {
		console.log(val.bcontent);
	}
}