Re: Const constructor
Francis Glassborow wrote:
Dragan Milenkovic wrote:
I'm not sure how was the necessity recognized in this thread.
And I still don't understand how could one design a class
that has copy/assignment and in the same time a const constructor.
const int x = 5;
const A a1(x);
A a2(a1);
a2.get() = 10; // ... and const_cast has bitten you data!!!
Sorry, but I do not understand the problem. Obviously you should not be
"A" is what OP was trying to design...
Fabio wrote:
struct A {
A( int* a) : x(a) {}
const A( const int* a) : x( const_cast<int*>(a) ) {}
const int& get() const { return *x; }
int& get() { return *x; }
int *x;
};
The problem is "A a2(a1)" creates a mutable object from a const one,
which allows "x" to be written to. But see below first...
able to assign to a const object but what is the problem with copying
it? There is no reason in general why a copy of a const object should
itself be const (and no reason that it shouldn't). The problem arises if
your class has pointer and/or reference members but such classes are
good examples of where having const qualified ctors might be useful.
I have no idea who is saying what. I'm totally confused.
Shall we start from the beginning? You speak about necessity of const
constructors. My assumption based on your words is that you would
create an additional const copy-ctor that would forbid the problematic
line "A a2(a1)", right? Would you be so kind as to write a complete
class based on OP's one? I still don't get how the whole picture
looks like. Someone provided a link to a proposal for const-ctor,
but it didn't cover these issues I ask about.
Thanks.
--
Dragan
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