[Issue 20424] A constructor with a value argument of the same type as being constructed should be an error

https://issues.dlang.org/show_bug.cgi?id=20424 RazvanN <razvan.nitu1305@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |razvan.nitu1305@gmail.com --- Comment #1 from RazvanN <razvan.nitu1305@gmail.com> --- This issue is invalid. That is not a copy constructor, it is a normal constructor so there is no threat of entering in infinite recursion. The reason why it works is that the compiler simply blitts the contents of a into the stack of the constructor. I don't see any problem with this. --

June 17, 2020

Posted by RazvanN

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RazvanN

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https://issues.dlang.org/show_bug.cgi?id=20424

RazvanN <razvan.nitu1305@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #5 from RazvanN <razvan.nitu1305@gmail.com> ---
(In reply to Walter Bright from comment #2)
> An object with a copy constructor cannot be blitted into place. (Such is not allowed in C++, either, and such constructors are rejected by the compiler.)
> 
> There is no advantage to doing it anyway over passing by ref.

Yes there is. You may want to construct from an rvalue, therefore you cannot
use a copy constructor since rvalue references are not yet implemented in the
language (there is a switch but it is only half implemented). `this(S)` does
exactly that. Of course, it is illegal to have both this(S) and this(ref S).

We discussed this extensively in the DIP.

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