Why it doesn't compile in D 2.0?

[Lutger]

On 01/16/2010 02:01 PM, aarti_pl wrote:
> W dniu 2010-01-16 13:26, Simen kjaeraas pisze:
>> aarti_pl <aarti at interia.pl> wrote:
>>
>>>
>>> class Test {
>>> string t1 = "test"; //Ok!
>>> char[] t2 = "test".dup; //Compile error
>>> }
>>>
>>> void main(char[][] args) {
>>> }
>>>
>>> Error:
>>> hello.d(3): Error: cannot evaluate _adDupT((&
>>> D12TypeInfo_Aya6__initZ),"test") at compile time
>>> hello.d(3): Error: cannot evaluate _adDupT((&
>>> D12TypeInfo_Aya6__initZ),"test") at compile time
>>>
>>> Is there workaround?
>>
>> Constant strings are saved in the static data segment of the
>> executable, so
>> the .dup call would need to be executed at runtime. In other words, what
>> this would do is cast const to mutable.
>>
>> If this did compile, changing the contents of t2 would change those
>> contents
>> for all instances of Test, which I assume is not your intention.
>>
>> As for the workaround, write a constructor:
>>
>> class Test {
>> string t1 = "test";
>> string t2;
>>
>> this( ) {
>> t2 = "test".dup;
>> }
>> }
>>
>
> I want just simple initialization of variable. Casting of course is no
> (sane) option.
>
> Indeed, in case of classes your workaround will work.
>
> But in case of struct? The same problem occurs for structs, but you can
> not declare default constructor in structs...
>
> IMHO .dup should work for initialization of classes/structs.
>
> Any other ideas?
>
> BR
> Marcin Kuszczak
> (aarti_pl)

Perhaps this is or should be a bug. You can override dup to work in ctfe:

char[] dup(string str)
{
     return str.dup;
}

class Test {
     string t1 = "test";        //Ok!
     char[] t2 = "test".dup;    //Compile error
     char[] t3 = "test".dup();  //Ok!
}

The spec even mentions it under ctfe:

6. as a special case, the following properties can be executed at 
compile time:
.dup
.length
.keys
.values

http://www.digitalmars.com/d/2.0/function.html