Copy constructor in D. Why it is necessary to have it.

[Denis Koroskin]

On Tue, 30 Sep 2008 23:37:50 +0400, Eldar Insafutdinov  
<e.insafutdinov at gmail.com> wrote:

> http://www.everfall.com/paste/id.php?m46jrb36o7qu
>
> This is a short example. It has all the comments inside. Since "in"  
> keyword tells the compiler to make a copy of an class object - a new  
> object is created.

No, that's not true. No heap activity is done under the hood, a copy of  
/pointer/ is passed (as opposed to a copy of /instance/).
In means that changes to the variable won't be visible to the caller:

void foo(in TreeIter it)
{
     it = null; // makes local change
}

An important thing to note is that `in` is not recursive (as const or  
invariant).

> But constructor for this object is not called(you can check it). In my  
> opinion it is a big issue and needs to be improved.

No, it shouldn't generate heap activity unless really needed. In this case  
do the following:

void foo(const(TreeIter) it)
{
     auto itCopy = it.clone();
     // do whatever you wish with a copy.
}

But in general, a const reference should be enough to you.