string - 如何使用 Swift 修改字符串中的单个字符？

Question

var str: String = "sometext"

for i in str.characters.indices
{
    str[i] = "c"
}

print(str)

我收到以下错误:
错误:无法通过下标赋值:下标是 get-only

Answer 1

您收到此错误是因为 Swift String 的下标方法是 get-only 就像它在您的警告中所说的那样。这与数组不同。

• 数组:

  数组[0] ✅

  array[0] = 0 ✅

• 字符串:

  str[0] ❌

  str[0] = "0" ❌

  str[str.startIndex.advancedBy(0)] ✅

使用 replaceRange 完成您的任务。

示例:

var value = "green red blue"

value.replaceRange(value.startIndex.advancedBy(
    6)..<value.startIndex.advancedBy(6 + 3),
    with: "yellow")
print(value)

结果:

green yellow blue

另请参阅 Ole Begemann 的这篇精彩博客文章，其中非常详细地解释了 Swift 字符串的工作原理。您还将找到为什么不能在 Swift 字符串上使用下标方法的答案。

Because of the way Swift strings are stored, the String type does not support random access to its Characters via an integer index — there is no direct equivalent to NSStringʼs characterAtIndex: method. Conceptually, a String can be seen as a doubly linked list of characters rather than an array. Article Link