Re: std::vector anomally
On Sat, 15 Dec 2007 20:59:52 GMT, "John Keenan"
<john.removeme.keenan@optimapowerware.com> wrote:
Const used so compiler error is generated when it is used as l-value.
Reference used so only address (pointer with different syntax) is passed as
argument. Often call stack is very deep and class has many member variables.
Perhaps simplied example shown did not warrant but it is single convention
we use.
But for the built-in types, there's no advantage to pass-by-const-reference
vs. pass-by-value, and it's conventional to use pass-by-value.
Pointers variables always used as class members so .h (class definition)
only uses forward declarations of class members and method arguments. Only
exception is member variables of "built in" types such as float, double,
int, etc. The purpose is to create decoupled .h files for easier maintenance
and faster compilation. User code only includes what it needs as opposed to
what the included .h needs.
That's a good goal, but isn't it difficult to apply it to types like
std::vector<bool>? I mean, there is <iosfwd>, but no <vectorfwd>, so you'd
have to look into <vector> and copy its declaration, repeating this for
every type you use. Perhaps a better approach is the pimpl idiom, which
would look something like this for your class:
class Xxx
{
private:
class Impl;
Impl* pimpl;
public:
Xxx();
virtual ~Xxx();
bool readOnly(unsigned i) const;
private:
// Copyguard
Xxx(const Xxx&);
void operator=(const Xxx&);
};
Then your .cpp file would look something like:
#include <vector>
class Xxx::Impl
{
public:
std::vector<bool> m_readOnly;
};
Xxx::Xxx()
: pimpl(new Impl)
{
}
Xxx::~Xxx()
{
delete pimpl;
}
bool
Xxx::readOnly(unsigned i) const
{
return pimpl->m_readOnly.at(i);
}
--
Doug Harrison
Visual C++ MVP