Bug? Const Class Makes Constructor Const

[Steven Schveighoffer]

On 10/25/18 4:39 PM, Vijay Nayar wrote:
> I suppose const(Bob) is a type in this case.  I guess I'm not sure what 
> the purpose of having a const constructor is. 

The main purpose is if you have const members that have to be assigned 
from const data.

For example:

class C
{
    int *ptr;
    this(int *p) { ptr = p; }
}

If you want to construct a const(C) with a const(int)*, you need a const 
constructor:

this(const(int *)p) const { ptr = p; }

I don't see how else you would do it.

> I see the benefit of 
> having const members, to assure that the object is not modifed after 
> creation, but when the constructor is const as well, that enforces 
> head-const behavior as well, so that whenever a reference variable is 
> initialized, that it cannot later reference something else.

Then you want a class that has tail-const data, not a const class.

> Maybe it's just best that I avoid this feature and don't put const in 
> front of the class.

Yeah, a const class is existentially unchangable after construction.

-Steve