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digitalmars.D.learn - standard alias for a class name inside the class code?

reply dan <dan.hitt gmail.com> writes:
Is there a standard alias for a class name inside class code?

Something like 'this' referring to a class instance, but 
referring instead to the class itself?

What i would like to do is have something like

class Clas {
    // alias Clas THIS; <- don't want this boilerplate
    static THIS make_instance( .... ) {
        auto x = new THIS( );
        ....
        return x;
    }
}

This would be great for copy/paste, changing class names, and in 
general communicating your intention.

I'm guessing the answer is no, and that there's some compelling 
reason why a compiled language wouldn't want to provide this 
feature.  (But the php interpreter, whatever else is good or bad 
about it, does let you write 'new self(...)' and does the right 
thing with it.)

TIA for any clues.

dan
May 28 2016
parent reply Mithun Hunsur <me philpax.me> writes:
On Sunday, 29 May 2016 at 00:14:17 UTC, dan wrote:

 Is there a standard alias for a class name inside class code?

 Something like 'this' referring to a class instance, but 
 referring instead to the class itself?

 [...]


typeof(this) gets you the type of the current class. :)
May 28 2016
parent reply dan <dan.hitt gmail.com> writes:
On Sunday, 29 May 2016 at 00:28:13 UTC, Mithun Hunsur wrote:

 On Sunday, 29 May 2016 at 00:14:17 UTC, dan wrote:

 Is there a standard alias for a class name inside class code?

 Something like 'this' referring to a class instance, but 
 referring instead to the class itself?

 [...]


 typeof(this) gets you the type of the current class. :)


Great!!

Thanks Mithun!

That certainly works.

But i sure don't understand how.

Especially in a declaration like
     static typeof(this) make_instance( )
but also in the 'new typeof(this)'.  In both cases, 'this' 
doesn't even exist.

In fact, if you make a reference to this inside the static 
function make_instance(), you get an error:
'this' is only defined in non-static member functions, not 
make_instance

So the compiler itself states that 'this' is not defined.

But nevertheless, your method absolutely does work.

So i suppose i should not look a gift horse in the mouth, but i'm 
still puzzled.

Anyhow, thanks a million, because whether or not i understand 
your idiom, it is exactly what i need.

dan
May 28 2016
parent reply jhps <jhps jhps.jhps> writes:
On Sunday, 29 May 2016 at 00:48:20 UTC, dan wrote:

 Especially in a declaration like
     static typeof(this) make_instance( )
 but also in the 'new typeof(this)'.  In both cases, 'this' 
 doesn't even exist.



https://dlang.org/spec/declaration.html#Typeof

it's another 'this' that has not the same semantic as the 
reference holder.
Just like 'const' can have 3 meanings, 'this' also:

- this.member: typical usage, it hold the instance reference
- void foo(this T)(): template this parameter, T is typeof(this) 
where the template is used.
- typeof(this): you can use it in static func, this 'this' is not 
the 'this' instance.
May 28 2016
parent dan <dan.hitt gmail.com> writes:
On Sunday, 29 May 2016 at 02:44:33 UTC, jhps wrote:

 On Sunday, 29 May 2016 at 00:48:20 UTC, dan wrote:

 Especially in a declaration like
     static typeof(this) make_instance( )
 but also in the 'new typeof(this)'.  In both cases, 'this' 
 doesn't even exist.



 https://dlang.org/spec/declaration.html#Typeof

 it's another 'this' that has not the same semantic as the 
 reference holder.
 Just like 'const' can have 3 meanings, 'this' also:

 - this.member: typical usage, it hold the instance reference
 - void foo(this T)(): template this parameter, T is 
 typeof(this) where the template is used.
 - typeof(this): you can use it in static func, this 'this' is 
 not the 'this' instance.


OK, thanks JHPS for the detailed explanation of this construction 
Mithun pointed out, and also for the link.  It makes a lot of 
sense the way you put it.
May 28 2016