• Benjamin Thaut <code benjamin-thaut.de> Oct 12 2010
• "Denis Koroskin" <2korden gmail.com> Oct 12 2010
• Jonathan M Davis <jmdavisProg gmx.com> Oct 12 2010
• Jesse Phillips <jessekphillips+D gmail.com> Oct 12 2010
• Jonathan M Davis <jmdavisProg gmx.com> Oct 12 2010
• "Steven Schveighoffer" <schveiguy yahoo.com> Oct 14 2010

Benjamin Thaut <code benjamin-thaut.de> writes:

I want to have a mutable reference to a const object. So that I can 
reasign the reference but can not modifiy the object. Is this possible 
in D 2.0? I found tailconst in the const FAQ but as it is not 
implemented in D 2.0 I'm clueless how to realize this.

-- 
Kind Regards
Benjamin Thaut

"Denis Koroskin" <2korden gmail.com> writes:

On Tue, 12 Oct 2010 13:07:59 +0400, Benjamin Thaut  
<code benjamin-thaut.de> wrote:

 I want to have a mutable reference to a const object. So that I can  
 reasign the reference but can not modifiy the object. Is this possible  
 in D 2.0? I found tailconst in the const FAQ but as it is not  
 implemented in D 2.0 I'm clueless how to realize this.


For pointers:

const(int)* c = new int();
c = new int(); // reassign

For references:

import std.typecons;

Rebindable!(Object) o = new Object();
o = new Object();

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Tuesday 12 October 2010 02:07:59 Benjamin Thaut wrote:
 I want to have a mutable reference to a const object. So that I can
 reasign the reference but can not modifiy the object. Is this possible
 in D 2.0? I found tailconst in the const FAQ but as it is not
 implemented in D 2.0 I'm clueless how to realize this.


Use Rebindable!() in std.typecons. It's a struct which can hold a const or 
immutable object. When you want to reassign it, you merely assign it the new 
reference and a new struct is created to replace it.

Unfortunately, at this point, tail const has pretty much been decided to be too 
difficult implement and/or too difficult to do cleanly, so it's not in D and
likely 
never will be. If it's mentioned in the online docs, the docs need to be 
updated. It's been a long time since there was any kind of tail const in D.

- Jonathan M Davis

Jesse Phillips <jessekphillips+D gmail.com> writes:

Jonathan M Davis Wrote:

 Unfortunately, at this point, tail const has pretty much been decided to be
too 
 difficult implement and/or too difficult to do cleanly, so it's not in D and
likely 
 never will be. If it's mentioned in the online docs, the docs need to be 
 updated. It's been a long time since there was any kind of tail const in D.
 
 - Jonathan M Davis


What I have heard is that it can't be done syntactically for references. As
Denis shows you can do it with points (and arrays) but not object references.

There are many syntax suggestion threads so I suggest search for them before
bring it up again.

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Tuesday, October 12, 2010 15:27:41 Jesse Phillips wrote:
 Jonathan M Davis Wrote:
 Unfortunately, at this point, tail const has pretty much been decided to
 be too difficult implement and/or too difficult to do cleanly, so it's
 not in D and likely never will be. If it's mentioned in the online docs,
 the docs need to be updated. It's been a long time since there was any
 kind of tail const in D.
 
 - Jonathan M Davis


 What I have heard is that it can't be done syntactically for references. As
 Denis shows you can do it with points (and arrays) but not object
 references.
 
 There are many syntax suggestion threads so I suggest search for them
 before bring it up again.


Yes, you can do it with pointers, but not with references, and it causes 
problems for stuff like ranges. There have been several discussions on it over 
time, and Walter has pretty much said that it's not a feature that's going to 
happen. He spent too much time on it before without success to want to try at
it 
again.

- Jonathan M Davis

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

On Tue, 12 Oct 2010 18:54:49 -0400, Jonathan M Davis <jmdavisProg gmx.com>  
wrote:

 On Tuesday, October 12, 2010 15:27:41 Jesse Phillips wrote:
 Jonathan M Davis Wrote:
 Unfortunately, at this point, tail const has pretty much been decided  


 be too difficult implement and/or too difficult to do cleanly, so it's
 not in D and likely never will be. If it's mentioned in the online  


 the docs need to be updated. It's been a long time since there was any
 kind of tail const in D.

 - Jonathan M Davis


 What I have heard is that it can't be done syntactically for  
 references. As
 Denis shows you can do it with points (and arrays) but not object
 references.

 There are many syntax suggestion threads so I suggest search for them
 before bring it up again.


 Yes, you can do it with pointers, but not with references, and it causes
 problems for stuff like ranges. There have been several discussions on  
 it over
 time, and Walter has pretty much said that it's not a feature that's  
 going to
 happen. He spent too much time on it before without success to want to  
 try at it
 again.


If someone were to do the work, and the syntax was bearable, it might be  
considered.  I think Walter no longer wants to accept any ideas without  
proof that they will work -- he's already worked enough on trying to  
implement tail-const.

I personally think tail const is going to be a very important feature that  
will not be solvable via the library.  Tail-const ranges are going to be  
very important when it comes to things like collections.

-Steve