Re: [boost] tuple and virtual functions

Subject: Re: [boost] tuple and virtual functions
From: Christopher Jefferson (chris_at_[hidden])
Date: 2012-01-12 08:35:51

On 12 Jan 2012, at 13:30, Mark Snelling wrote:

> I'm having a problem with Boost.Tuple virtual functions. Consider the code
> below, I would have expected the output to be "B::foo()" but instead get
> "A::foo()". Am I missing something here?

Yes, if you copy a A&, you end up with an A. This is known as 'slicing', and can be a pain. It has nothing to do with boost, or tuple.

Chris

> 
> #include <boost/tuple/tuple.hpp>
> #include <iostream>
> 
> class A
> {
> public:
> virtual void foo()
> {
> std::cout << "A::foo()" << std::endl;
> }
> };
> 
> class B :public A
> {
> public:
> void foo()
> {
> std::cout << "B::foo()" << std::endl;
> }
> };
> 
> boost::tuple< A > make( const A& a )
> {
> return boost::make_tuple( a );
> }
> 
> 
> int main( int argc, char* argv[] )
> {
> B b;
> make( b ).get< 0 >().foo();
> 
> return 0;
> }
> 
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