Using inout keyword: is the parameter passed-by-reference or by copy-in copy-out (/call by value result)

Question

Question: Based on the information and discussion below: Are inout parameters passed-by-reference or by copy-in copy-out?

Answer 1

The next two paragraphs in the Language Reference describes it more in detail:

In-Out Parameters

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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.

As an optimization, when the argument is a value stored at a physical address in memory, the same memory location is used both inside and outside the function body. The optimized behavior is known as call by reference; it satisfies all of the requirements of the copy-in copy-out model while removing the overhead of copying. Do not depend on the behavioral differences between copy-in copy-out and call by reference.

So it's de facto "pass by reference"