read-only access to a data member

[gvdeynde]

Hi,

What's the "best" way to have an object ObjA of class A have read-access
(but not write-access) to a data member of object ObjB of class B. Class B
has a std::vector<T> as a datamember. ObjA should be able to get elements of
that vector and, if possible, a read-only (const?) reference to the vector
as such. Is it possible to do this without a classical ObjB.Get() member
function? Since, for the element-wise access, this extra indirection level
could be non-negligable; I think....

bye,
gert

[Jonathan Mcdougall]

gvdeynde wrote:

Hi,

What's the "best" way to have an object ObjA of class A have read-access
(but not write-access) to a data member of object ObjB of class B. Class B
has a std::vector<T> as a datamember. ObjA should be able to get elements of
that vector and, if possible, a read-only (const?) reference to the vector
as such. Is it possible to do this without a classical ObjB.Get() member
function? Since, for the element-wise access, this extra indirection level
could be non-negligable; I think....

You could give B a container interface, but with only const member
functions:

class B
{
public:
typedef std::vector<T> V;
typedef V::const_iterator const_iterator;

const_iterator begin() const
{
return v_.begin();
}

const_iterator end() const
{
return v_.end();
}

private:
V v_;
};
Jonathan

[tony_in_da_uk]

Jonathan's suggestion of const_iterators is good. As an aside, the
"classical get method" is perfectly fine too: after all, your vector
look ups run operator[] which is a fancy-named get method. As long as
it's defined inline, there's no cost after optimisation. Tony