Recently, I've been delving into a TypeScript utility type known as TupleUnion. This useful type came to my attention through a fascinating Twitter post, and I've observed it being utilized in various Stack Overflow solutions. Here's how the type is defined:
type TupleUnion<U extends string, R extends any[] = []> = {
[S in U]: Exclude<U, S> extends never ? [...R, S] : TupleUnion<Exclude<U, S>, [...R, S]>;
}[U];
To test this type, I experimented with it in the TypeScript playground using the provided example:
interface Person {
firstName: string;
lastName: string;
dob: Date;
hasCats: false;
}
type keys = TupleUnion<keyof Person>;
The results were as expected. However, upon introducing additional properties to the Person interface:
interface Person {
firstName: string;
lastName: string;
dob: Date;
hasCats: false;
a: string;
b: string;
c: string;
d: string;
e: string;
f: string;
}
I encountered an error in TypeScript:
Type instantiation is excessively deep and possibly infinite.(2589)
This raised questions about why this utility type functions smoothly for others but triggers errors when expanding the interface with more properties. Could there be a limit to the number of properties that TupleUnion can manage, or might there be something overlooked?
If you have any insights or suggestions on resolving this dilemma, your input would be highly valued.