Private constructor

[Jeff Schwab]

Re: Private constructor

Andy wrote:
[color=blue]
> Constructors do have this pointers. Got that corrected. "This" can be
> accessed inside the constructor body, not the initializer list ...
> which is absolutely logical. In the initializer list, the object is
> still to be completely constructed.[/color]

The same may be said of the entire constructor, if the class has virtual
methods.

Thanks for helping explain why constructors cannot be called.

-Jeff

[Mike Hewson]

Re: [Nit] Re: Private constructor

"Ron Natalie" <ron@sensor.com > wrote in message
news:3fe56b94$0 $472$9a6e19ea@n ews.newshosting .com...
<snip>

So, *evidently* it is the difference between implicit and explicit uses of
the constructor ie. can I name it ( no choice really ) and call it by that
name in the source code outside it's definition in the class ( no ), or will
the implementation of the abstract/virtual machine invoke the constructor's
code ( well, 'as if' anyway ) upon any given instantiation ( including
temporaries, classes composing classes etc ... ) ?

Cheers
--
Hewson::Mike
"This letter is longer than usual because I lack the time to make it
shorter" - Blaise Pascal

[Ron Natalie]

Re: [Nit] Re: Private constructor


"Mike Hewson" <hewsmike@austa rnet.com.au> wrote in message news:bs683b$f3e $1@austar-news.austar.net .au...
[color=blue]
> So, *evidently* it is the difference between implicit and explicit uses of
> the constructor ie. can I name it ( no choice really ) and call it by that
> name in the source code outside it's definition in the class ( no )[/color]

You can't name it. The standard says they don't have names just a
convention for declaring/defining them. This is important as it resolves
an ambiguity between whether it is a type name or the consturctor
name (by eliminating the latter).

Frankly, it's C++'s terseness and eschewing of additional reserved
words.

Since constructors NEVER participate in name resolution, there is
NO way to reference it so it can be called. You always get a class
name when you try so it always thinks that you are doing a cast.
[color=blue]
> or will
> the implementation of the abstract/virtual machine invoke the constructor's
> code ( well, 'as if' anyway ) upon any given instantiation ( including
> temporaries, classes composing classes etc ... ) ?[/color]

That is true. Any time you create an object either by invocation of new,
defining a variable of that type, creation of a temporary, function arguments,
subobjects of a larger object, etc... the compiler invokes the defined initialization
on the object and all of its subobjects. For (most) classes this means invoking the constructor.
So it is more than just one constructor being run in most cases.

[Mike Hewson]

Re: [Nit] Re: Private constructor

"Ron Natalie" <ron@sensor.com > wrote in message
news:3fe69e7a$0 $465$9a6e19ea@n ews.newshosting .com...[color=blue]
> You can't name it. The standard says they don't have names just a
> convention for declaring/defining them. This is important as it resolves
> an ambiguity between whether it is a type name or the consturctor
> name (by eliminating the latter). Frankly, it's C++'s terseness and[/color]
eschewing[color=blue]
> of additional reserved words. Since constructors NEVER participate in name
> resolution, there is NO way to reference it so it can be called. You[/color]
always get[color=blue]
> a class name when you try so it always thinks that you are doing a cast.[/color]

Bingo! That makes perfect sense, 'of course' .... I say in retrospect. :-)

Thanks.

Cheers
--
Hewson::Mike
"This letter is longer than usual because I lack the time to make it
shorter" - Blaise Pascal

[Ron Natalie]

Re: Private constructor


"Jeff Schwab" <jeffplus@comca st.net> wrote in message news:q--dnabMl-wR8nui4p2dnA@co mcast.com...[color=blue]
> Andy wrote:
>[color=green]
> > Constructors do have this pointers. Got that corrected. "This" can be
> > accessed inside the constructor body, not the initializer list ...
> > which is absolutely logical. In the initializer list, the object is
> > still to be completely constructed.[/color]
>
> The same may be said of the entire constructor, if the class has virtual
> methods.
>[/color]
Virtualness is hotwired to the type of the constructor's class while the constructor
body is running. It's no more or less of a problem with virtual methods than
anything else. It's always incumbent on code executing during construction
to be aware of what has and has not been initialized so far.

The only issue is that passing "this" outside the constructor context is a warning
sign that someone ignorant of the fact that the object is still under construction
may do something inappropriate. The compiler is just warning you to look
further.