public or private inheritance of boost::noncopyable?

[lbonafide]

Every example I see (including on boost:rg) of using noncopyable
involves inheriting from it privately. Is there a drawback from
inheriting publicly? Is it just that it's not a good example of and
"is-a" relationship?

#include <boost/utility.hpp>

class A : public boost::noncopyable {};

int main()
{
A a;

A b(a);

return 0;
}

g++ -Wall -I\boost_1_33_1 -c noncopy.cpp

noncopy.cpp: In copy constructor `A::A(const A&)':
/boost_1_33_1/boost/noncopyable.hpp:27: error:
`boost::noncopyable_::noncopyable
::noncopyable(const boost::noncopyable_::noncopyable&)' is private
noncopy.cpp:9: error: within this context

 

[Alan Johnson]

Every example I see (including on boost:rg) of using noncopyable
involves inheriting from it privately. Is there a drawback from
inheriting publicly? Is it just that it's not a good example of and
"is-a" relationship?

You've pretty much answered the question already. You don't want people
making a function like:

void profoundlyUselessFunction(const boost::noncopyable &);

The typical use of boost::noncopyable is a "implemented in terms of"
relationship, which is best modeled by inheriting privately.

From a technical standpoint, since everything interesting in
boost::noncopyable is private already, whether you inherit publicly or
privately makes very little difference.

 

[Alexander Dong Back Kim]

You've pretty much answered the question already. You don't want people
making a function like:

void profoundlyUselessFunction(const boost::noncopyable &);

The typical use of boost::noncopyable is a "implemented in terms of"
relationship, which is best modeled by inheriting privately.

From a technical standpoint, since everything interesting in
boost::noncopyable is private already, whether you inherit publicly or
privately makes very little difference.

That was a great answer =)

cheers,