Why does C++ not have a const constructor?

Question

(Edit: Heavy change because previous example was flawed, which may make some answers/comments seem odd)

This might be an overly contrived, but the following

Answer 1

In my opinion, the fact of that the ctors haven't return-type specification is what fails here. Any other imaginable syntax like for example

class A
{
    const A& ctor(...);
}

would be, imho, very valuable. For example, imagine such a situation of calling a method with prototype

void my_method(const my_own_string_class& z);

If my_own_string_class holds a ctor from char*, the compiler could choose this ctor, but as this ctor is not allowed to return a const object, it need to allocate and copy... If const return type were allowed, one could do

class my_own_string_class
{
    char *_ptr;
    public:
    const my_own_string_class& ctor(char *txt)
    : _ptr(txt)
    { return *this;}
 }

provided that this special construct be restricted to the creation of temporal instances. (And dtor's must be mutable ;) ).