Variadic Tuple Types

１つ目の変更

タプルのspreadがgenericになった

code:ts

function tail<T extends any[]>(arr: readonly any, ...T) {

return rest;

}

const myTuple = 1, 2, 3, 4 as const;

const myArray = "hello", "world";

const r1 = tail(myTuple);

// ^ = const r1: 2, 3, 4

const r2 = tail(...myTuple, ...myArray as const);

// ^ = const r2: [2, 3, 4, ...string[]]

２つ目の変更

rest elementsがタプル内のどこでも使えるようになった

code:ts

type Strings = string, string;

type Numbers = number, number;

これが型でできるようになった

従来は末尾でしかできなかった

concatの型定義もこのとおり

code:ts

type Arr = readonly any[];

function concat<T extends Arr, U extends Arr>(arr1: T, arr2: U): ...T, ...U {

}

code:ts

type Arr = readonly unknown[];

function partialCall<T extends Arr, U extends Arr, R>(

f: (...args: ...T, ...U) => R,

...headArgs: T

) {

return (...tailArgs: U) => f(...headArgs, ...tailArgs);

}

部分適用の型もしっかり通る