Copy Constructor DIP

[Jonathan M Davis]

On Tuesday, 10 July 2018 14:58:09 MDT Manu via Digitalmars-d wrote:
> 2. It looks like copy constructors are used to perform assignments
> (and not constructions)... but, there is also opAssign. What gives?
>     Eg:
>       S b = a; // <- copy construction? looks like an assignment.
>     And not:
>       S b = S(a); // <- actually looks like a construction, but this
> syntax seems to not be intended (and rightly so, it's pretty terrible)

S b = a;

has never been assignment in either C++ or D. It's initialization /
construction, which means that it calls a constructor - be that a postblit
constructor or a copy constructor. Assignment only occurs when you're giving
an existing object a new value.

And why would

S b = S(a);

not be intended? Sure, it's kind of pointless if a is an S, but if you have
a copy constructor, it makes perfect sense that S(a) would work and would be
pretty bizarre if it didn't, since it's explicitly calling the copy
constructor. It even works right now if you give S a constructor that takes
an S. It just isn't actually treated as a proper copy constructor at the
moment, since that's currently the postblit constructor's job.

- Jonathan M Davis