arrays - "inout"是否影响数组的写复制行为？

Question

我认为 inout 让你传入一个引用(准确吗？)，然后如果引用被多次更改，就像你可能对数组所做的那样，那么数组就不必复制很多次，因为它现在是一个引用类型？

Answer 1

swift 中输入输出参数的语义不同于通过引用传递值。以下是传递输入输出参数时发生的情况:

In-out parameters are passed as follows:

1. When the function is called, the value of the argument is copied.
2. In the body of the function, the copy is modified.
3. When the function returns, the copy’s value is assigned to the original argument.

This behavior is known as copy-in copy-out or call by value result. For example, when a computed property or a property with observers is passed as an in-out parameter, its getter is called as part of the function call and its setter is called as part of the function return.

参见 https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/doc/uid/TP40014097-CH34-ID545

数组在 swift 中是值类型，因此在这种情况下它被完全复制。当然，swift 编译器可能会对其进行优化，但无论如何，您可以保证看到与执行完整副本时完全相同的行为。