打字稿将元组的类型元组转换为元组(扁平元组)

问题描述：

我有这个

Type T = Params<[Tuple1, Tuple2]> // eg [[string], [number]]

如何制作(压扁)

Type Flatten<T> = Params<[string, number]>

答

我们可以通过映射类型来做到这一点.考虑代码:

We can do that by mapped types. Consider the code:

type T = Params<[Tuple1, Tuple2]>

// utility type
type Flatten<T extends any[]> = {
  [K in keyof T]: T[K] extends any[] ? T[K][0] : T[K]
}
type Result = Flatten<T>
// evaluates into [string, number]

const a: Result = ['a', 1] // correct value of the type

注意Flatten 的工作原理:

[K in keyof T] - 意味着我们想要所有的键，所以在元组中说元素
T[K] 扩展 any[] ?T[K][0] : T[K] - 我们说如果给定键上元素的值是一个数组，那么给我这个数组的第一个元素的类型(索引 0)，如果不要保持原样，因为没有什么可压扁的

[K in keyof T] - means we want to have all keys, so in tuple say elements
T[K] extends any[] ? T[K][0] : T[K] - we say if the value of the element on the given key is an array then give me a type of an first element of this array (index 0), if not leave it as is, as there is nothing to be flatten

如果您的元组考虑了不止一种类型的元素，那么上述解决方案将仅采用第一种.所以对于元组 [string, number] 它将产生 string.如果我们想在元组中收集所有可能的类型，我们可以创建更复杂的类型.考虑:

If your tuples consider more then one type of the element, then above solution will take the first only. So for tuple [string, number] it will produce the string. If we want to gather all possible types inside the tuple we can create more sophisticated type. Consider:

type Flatten<T extends any[]> = {
  [K in keyof T]: T[K] extends any[] ? T[K][Exclude<keyof T[K], keyof any[]>] : T[K]
}

T[K] 扩展 any[] ?T[K][Exclude<keyof T[K], keyof any[]>] : T[K] 意味着如果我们的元素是一个数组，那么获取所有元素的类型，但删除值的类型在数组原型中.

T[K] extends any[] ? T[K][Exclude<keyof T[K], keyof any[]>] : T[K] means that if our element is an array then get me types of all elements, but remove types of values in array prototype.

在结果 Flatten> 中将产生 [string |号码].所以这取决于你的目标是什么.

In the result Flatten<Params<[string, number]>> will produce [string | number]. So it depends what is your goal.

最后一个命题是，如果不考虑其他类型而只考虑嵌套数组/元组，我们可以避免条件类型.考虑最后一个解决方案:

The last proposition is, if you don't consider other types and only nested array/tuples, we can avoid conditional types. Consider last solution:

type Flatten<T extends E[], E extends any[] = any[]> = {
  [K in keyof T]: T[K][Exclude<keyof T[K], keyof any[]>]
}

以上类型限制更多，因为它仅适用于 [[]] 但更简洁和具体.

Above type is more restrict as it works with only [[]] but is more concise and specific.

打字稿将元组的类型元组转换为元组(扁平元组)

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