Allow mapped tuples to have behaviour based on index

Search Terms

mapped tuples index

Suggestion

I want to be able to create a tuple from function parameters and have all elements in the tuple optional other than the firstK

Use Cases

I am trying to create a curry implementation that allows you to curry any number of parameters. The first parameter must be specified but all other params are optional.
Would be good to be able to remove the last param as well.

Examples

something along the lines of

type OptionalExceptFirst<T> = {
    [K in keyof T]:isFirst ? ? T[K] : T[K];
};
type AllExceptLast<T> = {
    [K in keyof T]:isLast ? never : T[K];
};

The syntax will need some work hopefully the intended functionality is clear.

Checklist

My suggestion meets these guidelines:

• [x ] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [ x] This wouldn't change the runtime behavior of existing JavaScript code
• [ x] This could be implemented without emitting different JS based on the types of the expressions
• [ x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• [ x] This feature would agree with the rest of TypeScript's Design Goals.

La issue non indica file, test o punti di ingresso, quindi esamina innanzitutto il comportamento attuale delle tuple mappate e il modo in cui TypeScript rappresenta le posizioni delle tuple. Chiarisci le regole previste per l’optionalità in base al primo e all’ultimo indice prima di proporre l’implementazione e i test; per considerare il lavoro completato sarebbero necessari un design concordato e un comportamento del compilatore validato.