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.

この issue ではファイル、テスト、エントリポイントが指定されていないため、まず現在の mapped tuple の挙動と、TypeScript が tuple の位置をどのように表現するかを確認してください。実装とテストを提案する前に、最初と最後のインデックスに基づく optionality の意図されたルールを明確にしてください。完了とするには、合意された設計と、検証済みのコンパイラーの挙動が必要です。