what is the diffrence between <T> and <T, _>

[luckydog]

i can't understand

[KDragon]

Hi @luckydog12, you can identify an example so your question can be answered precisely !

[luckydog]

const clone = <T, _>(arr: T[]): T[] => [...arr]
i try to ignore _ , use < T > like this: const clone = < T > (arr: T[]):T[] => [...arr]
it also work, so i don't know _ for what?????
can u understand what i mean ?

[Becker Sun]

@luckydog12 <T, _> 相当于是2个参数类型的泛型约束，就像 <T, U> 写法一样，只是这里第二个参数类型约束没用上，因为你的示例代码只有一个参数，如果把你的示例改改，可能就好理解了。
比如：const clone = <T, _>(arr:T[], arr2:_[]):(T|_)[] => [...arr, ...arr2]
等同于：const clone = <T, U>(arr:T[], arr2:U[]):(T|U)[] => [...arr, ...arr2]