Swfit - 使用范围运算符，奇怪行为将项添加到数组

Question

在swift playground中，此代码可以正常工作：

ul#menu-mainmenu {
display:table;
width: 100%;
margin:0 0;}
ul#menu-mainmenu li {
 width: auto;              
 margin: 0 30px 0 20px;}

但是，如果我们 REPLACE 下面四行中的每一行，上面的第二行，则不会生成编译错误，但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. 不打印任何内容：

shoppingList.count

对我而言，如果由于某种原因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! 正在附加到数组中，那么上面三行中的至少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不是具有4个元素的数组的有效索引。

如果你想使用下标setter附加到数组 （“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，也可以使用+=或appendContentsOf()。