How are extra copy constructor parameters used?

[Paul Backus]

On Thursday, 30 December 2021 at 02:04:30 UTC, Ali Çehreli wrote:
> On 12/29/21 5:14 PM, Paul Backus wrote:
>
>> Therefore, when you write your own copy constructors, you 
>> should always use `inout` if possible, so that 
>> compiler-generated copy constructors will be able to copy 
>> instances of your struct that appear as members of other 
>> structs.
>
> Excellent point. I noticed a typo in the documentation:
>
> struct A
> {
>     this(ref return scope inout A rhs) immutable {}
> }
>
> That 'immutable' should be 'inout', right?

I think 'immutable' is correct here, since the usage examples 
look like this:

     A r1;
     const(A) r2;
     immutable(A) r3;

     // All call the same copy constructor because `inout` acts 
like a wildcard
     immutable(A) a = r1;
     immutable(A) b = r2;
     immutable(A) c = r3;