Re: non-const refs to const objects
On Apr 30, 4:13 am, gnepp...@web.de wrote:
Hi all,
as I've come to learn it, casting away constness from objects that are
actually const results in Undefined Behaviour.
The safe way of modifying data members from within const member
functions is declaring the data member "mutable".
So what about the following code which uses neither suspicious-looking
"const_casts" nor "mutable", and still modifies a const object. Is it
UB? I'm confused...
struct Bar
{
Bar()
{
mutable_this = this;
}
void modify() const
{
mutable_this->value=42;
}
Bar* mutable_this;
int value;
};
const Bar bar;
int main()
{
bar.modify();
}
This is OK for two reasons:
* in a "const" method the "this" get to a "const Bar*" to the class
while "mutable_this" remains a "Bar*"
* the change to "mutable_this->value" is legal since in the const
method what you were not allowed to change was the pointer not the
pointed value.
So, this is OK:
void modify() const
{
mutable_this->value=42;
}
while this NOT:
void modify() const
{
mutable_this=new Bar();
}
Cheers,
-- Marco
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