Not addressing the question mark syntax, my inquiry pertains to the usage of -? in scenarios such as the following:
type Required<T> =
T extends object
? { [P in keyof T]-?: NonNullable<T[P]>; } // <---------- "-?" here
: T;
Referenced from a 2018 GitHub comment, this particular syntax seems absent from TypeScript's guide on advanced types and utility types.
The usage of -? displayed above successfully compiles in TypeScript 3.8 and serves as the opposite of ?, essentially requiring the key. Is it similar to Required? If not, what is the specific name for this syntax and where can one find further information about it?