ios - 如果常量是不可变的，为什么我可以使用 let 重新分配它们？

Question

来自 Apple 文档“Learn the Essentials of Swift”

A constant is a value that stays the same after it’s declared the first time, while a variable is a value that can change. A constant is referred to as immutable, meaning that it can’t be changed, and a variable is mutable. If you know that a value won’t need to be changed in your code, declare it as a constant instead of a variable.

但在 REPL 中，我可以这样做:

 14> let favoriteNumber = 4
favoriteNumber: Int = 4
 15> let favoriteNumber = 5
favoriteNumber: Int = 5

我显然遗漏了一些东西:这种差异是否与编译器或运行时有关，还是其他原因？

Answer 1

您可以在 REPL 中完成您在普通代码中无法完成的事情。

您不能在 playground 或编译代码中重新分配常量。

我不确定这是 REPL 中提供的特殊便利，还是一个错误。