const in dmd v2.011

[Jason House]

Derek Parnell wrote:

> On Wed, 20 Feb 2008 19:03:56 -0500, Jason House wrote:
> 
>> It seems like you may have read some very early D 2.x docs on const and
>> not
>> read the later D 2.x docs.  The const design has changed a lot.
> 
> Thanks Jason. I know that keeping up with the changes in const theory and
> practice is a full time job in itself ;-) but I had been aware of these
> later tweaks.
> 
>> Derek Parnell wrote:
>>> Observations:
>>> ** It appears that there is no practical difference between 'const(C) c'
>>> and 'const C c'.
>> 
>> This is the definition of transitive const.
> 
> Yes it is. What I was bring to attention is the potentially confusing
> syntax options that are now available.

I don't see the confusion.  I've previously argued that "const(C) c"
and "const C c" should mean the same thing.  The whole distinction between
a type and a storage class seemed foreign and strange to me.



>>> ** It appears that 'const(char[])' and 'const const(char)[]' are
>>> equivalent and also not implemented well (or the error messages are just
>>> bad).
>> 
>> const(char)[] means the char's within the array can't be changed, but the
>> array itself can change (ie. length changes, concatenation)
> 
> Yes, I know what it means.

Sorry.  It's tough to know what people know, and it's usually best to
elimate the simple stuff first ;)


> Again what I'm bring attention to is the 
> confusing nature of this syntax.
> 
>    const(char)   X; // 'X' is const.
>    const(char)[] X; // 'X' is not const.
> 
> also this ...
> 
>    const(char)* k; // 'k' is a mutable pointer to immutable data.
>    const(char*) l; // 'l' is an immutable pointer to immutable data.
> 
> The forms 'const(char)[]' and 'const(char)*' ignore transitivity while
> other forms enforce it. It could be confusing, no?

I've already admitted that I'm biased :)  It seems easy to explain to me:
* Anything inside parenthesis is constant
* Const is transitive.  Any data access through a const reference is const.
* "const T t" is the same as "const(T) t"



> Also the forms 'const const(X)[]', 'const const(X[])', and 'const(X[])'
> appear to be synonymous, another way to confuse people.

I totally agree with that.  Literally typed like that seems like it should
be illegal.  I can imagine complex cases where something like that should
be legal...  eg:  alias const(X) Y; const Y z;