Latest const expansion

[Yigal Chripun]

Regan Heath wrote:
> I'm interested in what people think of the idea(s) I had for expanding 
> on Walter's latest const proposal and handling head/tail const on class 
> references.
> 
> Ideas originally posted as replies, here:
> 
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=58107 
> 
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=58112 
> 
> 
> Also here:
> 
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=58114 
> 
> http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=58115 
> 
> 
> 
> In short, Where:
> 
> head const - means the class reference itself cannot be modified
> tail const - means the class members cannot be modified
> 
> Where T is a class:
> 
> const(T)  indicates both head/tail const
> const(*T) indicates tail const
> const(&T) indicates head const
> 
> Eg.
> 
> class A { int a; }
> 
> const(A)  a;  //a cannot be modified, a.a cannot be modified
> const(*A) b;  //a can be modified, a.a cannot be modified
> const(&A) c;  //a cannot be modified, a.a can be modified
> 
> The idea being that const(*T) means const("value of the type T") where 
> the value of a class reference is the class instance itself.  Likewise 
> const(&T) means const("reference/pointer of the type T") indicating the 
> reference is to be const.
> 
> For template/meta-programming purposes the syntax "const(*T)" and 
> "const(&T)" should be legal for T where T is a value type, i.e. struct, 
> union, and primitives (excluding pointers) but will be identical in 
> behaviour to "const(T)"
> 
> 
> For pointers and arrays the "const(*T)" (tail const) syntax is not 
> required as we can say:
> 
> const(T)[]
> const(T)*
> 
> but perhaps for meta-programming purposes it should be legal, eg.
> 
> const(*char[])
> const(*char*)
> 
> 
> For pointers and arrays the "const(&T)" (head const) syntax is required 
> as there is currently no way to get a const array reference to mutable 
> data, so:
> 
> const(&char[])
> const(&char*)
> 
> would specify a const array reference and const pointer respecitvely 
> both to mutable 'char' data.
> 
> Thoughts?  Too complicated?  :P
> 
> Regan

Hello,
I'm a new user of D.
I've read about the const system and i agree with everyone who wants a 
head/tail const. however i disagree with the sytax proposed by various 
people as being unreadable.
const(*char*) or const (&char**) is quite confusing in my opinion.

my proposal is to simply use the terms tail/head, so the syntax will be
[head|tail] const (T) | const T

for example:
head const (C) c; // c is const but c.x isn't
tail const (C) c; // c is mutable but c.x is const
const (C) c; // as before, both c and c.x are const
head const C c; // Error
tail const C c; // Error

Yigal Chripun