英文:
How to perform operations on union of array types?
问题
以下不起作用
type Foo = number[]
type Bar = string[]
function move(x: Foo | Bar) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
因为显然 v 是 number[] | string[] 类型，不能分配给数字或字符串。我该如何解决这个问题？
英文:
The following doesn't work
type Foo = number[]
type Bar = string[]
function move(x: Foo | Bar) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
Because apparently v is number[] | string[] and is not assignable to either number or string. How do I work around this?
答案1
得分: 1
如果类型无关，使用 unknown
由于这是对数组进行完全通用的操作（移动一些元素），数组的实际类型不重要。只需声明该函数接受任何unknown[]或Array<unknown>可以工作的数组即可：
type Foo = number[]
type Bar = string[]
function move(x: unknown[]) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
declare const arr: Foo | Bar;
move(arr); //OK
如果类型可能重要，使用泛型
如果也包括类型有意义，使用泛型并将其约束为仅限数组可能更合理：
type Foo = number[]
type Bar = string[]
function move<T extends Array<unknown>>(x: T) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
declare const arr: Foo | Bar;
move(arr); //OK
这可能对指定调用中期望的类型很有用，如果类型不匹配，它将引发编译错误：
move<string[] | number[]>(arr); // OK
move<string[] | number[] | boolean[]>(arr); // OK
move<string[] | boolean[]>(arr); // error
move<string[]>(arr); // error
英文:
Use unknown if the type does not matter
Since this is a completely generic operation on an array (moving some elements), the actual type of the array is irrelevant. It is enough to declare that the function accepts any array where unknown[] or `Array<unknown> would work:
type Foo = number[]
type Bar = string[]
function move(x: unknown[]) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
declare const arr: Foo | Bar;
move(arr); //OK
Use a generic if the type may matter
If it makes sense to also include the type, use a generic and constrain it to only arrays:
type Foo = number[]
type Bar = string[]
function move<T extends Array<unknown>>(x: T) {
const v = x.splice(0, 1)
x.splice(1, 0, ...v)
}
declare const arr: Foo | Bar;
move(arr); //OK
This might be useful to specify the types expected in a call which will then raise a compilation error if they do not match:
move<string[] | number[]>(arr); // OK
move<string[] | number[] | boolean[]>(arr); // OK
move<string[] | boolean[]>(arr); // error
move<string[]>(arr); // error
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