Re: Avoid automatic copy constructor generation
On 27 Okt., 22:10, Pete Becker <p...@versatilecoding.com> wrote:
On 2008-10-27 16:30:13 -0400, Juha Nieminen <nos...@thanks.invalid> said:
One problem with copy constructors (if you have implemented one
explicitly) is that each time you add a new member variable to your
class, you have to remember to add it to the copy constructor (and
assignment operator). This is extremely easy to forget.
Testing will catch that.
Well - i certainly hope so ;-)
If the member
variable is just eg. an int, then it the default copying would be enoug=
h
for it, so calling the compiler-generated copy constructor would
automatically copy it without having to do anything special about it.
(The user-written copy constructor could then simply concentrate on the
members which do need special copying.)
So the default copy constructor would only copy members that were not
copied by the user-written one? How could it know?
I agree - that would not be possible. But can I sidestep a little and
be off-topic for a second? I really like the idea of having a copy-
constructor being default being defined explicitly with the new
syntax, and now I wonder if there has been any proposal to expand on
the default stuff, notable for swap.
As the user-defined copy-constructor really is error-prone (I have
been bitten once or twice by forgetting the copying when adding a new
member to a class), I do my best to make sure that the default
constructor (and assignment-operator) works and normally restrict my
userdefined constructors to small classes with less than a handfull of
membervariables. But swap is another matter: I normally don't write a
swap function and live with the lost performance, correcting the
problem when e.g. I wind up with sorting large arrays of those
objects. But wouldn't it be nice if you could write void
swap(my_class& other) = default as well?
In other words: has there been any proposal to provide this
functionality in some later version of C++? I have skimmed the docs
but found nothing like that in C++0x. I do not know how general it
could be: having "= default" creating a function with standard
functionality for each member-variable (causing an error when that
functionality is not available) would be nice indeed.
/Peter