D - more or less power than C++?

[Johan Granberg]

Hasan Aljudy wrote:
>> It is not const methods so much as const in parameters.
>>
>> class A
>> {
>>  int bar=1;//bar should bee read only
>> }
>>
>> void foo(in i a)//I want a to bee readonly
>> {
>>     i.bar=2;//here the value should not be writable but since a is
>>             //a reference it is
>> }
>>
>> A a=new A;//bar is 1
>> foo(a);
>> print(a.bar);//prints 2
>>
>> It is not so very usefull in smal examples but if you have a large 
>> program and do that by mistake it could cause a bug. Basicaly it is a 
>> message from the writer of a class to it's users of how member are to 
>> bee used, and aditionaly it has compiler suport to catch typos and 
>> mistakes, if a user realy want to change the data against the orginal 
>> authors recomendations he can use a explicit cast.
> 
> Maybe I'm missing something, but why don't you just mak A.bar private?

Because then i would have to call a method to read bar and that would 
bee inefective. I know it is no big deal when bar is only an ont but 
when larger structures is copied the overhead can bee a significant 
slowdown. also privat does not protect from misstakes in the same class 
but if you do a cast you will think about why it is readonly in the 
first place.