arrays - Swift - 使用范围运算符将项目添加到数组，奇怪的行为

Question

在 swift playground 中，这段代码工作正常:

shoppingList = ["item0", "item1", "item2", "item3"]
shoppingList[3...3] = ["item4", "item5", "item6"]
shoppingList.count // prints 6.
shoppingList // prints item0 through item6 (minus item3) in the shoppingList.

但是如果我们REPLACE下面四行中的每一行，上面的第二行，不会产生编译错误，但是shoppingList.count不会打印出任何东西:

shoppingList[3...4] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[3...6] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[4...6] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[3...5] = ["item4", "item5", "item6"] // Doesn't Work!

在我看来，如果出于某种原因 shoppingList[3...3] = ["item4", "item5", "item6"] 正在作为数组的 append 工作，这对我来说似乎是合乎逻辑的，至少上面三行中的一行应该可以正常工作。

Answer 1

全部

shoppingList[3...4] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[3...6] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[4...6] = ["item4", "item5", "item6"] // Doesn't Work!
shoppingList[3...5] = ["item4", "item5", "item6"] // Doesn't Work!

导致fatal error: Array index out of range因为4不是包含 4 个元素的数组的有效索引。

如果您想使用下标 setter 追加到数组(“拼接”)然后你可以使用 ..< 排除上限的范围运算符:

var shoppingList = ["item0", "item1", "item2", "item3"]

shoppingList[4 ..< 4] = ["item4", "item5", "item6"]
// ["item0", "item1", "item2", "item3", "item4", "item5", "item6"]

当然，+=或 appendContentsOf()也可以使用。