libs/ptr_container/test/tut1.cpp
//
// Boost.Pointer Container
//
// Copyright Thorsten Ottosen 2003-2005. Use, modification and
// distribution is subject to the Boost Software License, Version
// 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// For more information, see http://www.boost.org/libs/ptr_container/
//
//
// This example is intended to get you started.
// Notice how the smart container
//
// 1. takes ownership of objects
// 2. transfers ownership
// 3. applies indirection to iterators
// 4. clones objects from other smart containers
//
//
// First we select which container to use.
//
#include <boost/ptr_container/ptr_deque.hpp>
//
// we need these later in the example
//
#include <boost/assert.hpp>
#include <string>
#include <exception>
//
// Then we define a small polymorphic class
// hierarchy.
//
class animal : boost::noncopyable
{
virtual std::string do_speak() const = 0;
std::string name_;
protected:
//
// Animals cannot be copied...
//
animal( const animal& r ) : name_( r.name_ ) { }
void operator=( const animal& );
private:
//
// ...but due to advances in genetics, we can clone them!
//
virtual animal* do_clone() const = 0;
public:
animal( const std::string& name ) : name_(name) { }
virtual ~animal() throw() { }
std::string speak() const
{
return do_speak();
}
std::string name() const
{
return name_;
}
animal* clone() const
{
return do_clone();
}
};
//
// An animal is still not Clonable. We need this last hook.
//
// Notice that we pass the animal by const reference
// and return by pointer.
//
animal* new_clone( const animal& a )
{
return a.clone();
}
//
// We do not need to define 'delete_clone()' since
// since the default is to call the default 'operator delete()'.
//
const std::string muuuh = "Muuuh!";
const std::string oiink = "Oiiink";
class cow : public animal
{
virtual std::string do_speak() const
{
return muuuh;
}
virtual animal* do_clone() const
{
return new cow( *this );
}
public:
cow( const std::string& name ) : animal(name) { }
};
class pig : public animal
{
virtual std::string do_speak() const
{
return oiink;
}
virtual animal* do_clone() const
{
return new pig( *this );
}
public:
pig( const std::string& name ) : animal(name) { }
};
//
// Then we, of course, need a place to put all
// those animals.
//
class farm
{
//
// This is where the smart containers are handy
//
typedef boost::ptr_deque<animal> barn_type;
barn_type barn;
#if !defined(BOOST_NO_CXX11_SMART_PTR) && !(defined(BOOST_MSVC) && BOOST_MSVC == 1600) && !BOOST_WORKAROUND(BOOST_GCC, < 40600)
typedef std::unique_ptr<barn_type> raii_ptr;
#else
typedef std::auto_ptr<barn_type> raii_ptr;
#endif
//
// An error type
//
struct farm_trouble : public std::exception { };
public:
//
// We would like to make it possible to
// iterate over the animals in the farm
//
typedef barn_type::iterator animal_iterator;
//
// We also need to count the farm's size...
//
typedef barn_type::size_type size_type;
//
// And we also want to transfer an animal
// safely around. The easiest way to think
// about '::auto_type' is to imagine a simplified
// 'std::auto_ptr<T>' ... this means you can expect
//
// T* operator->()
// T* release()
// deleting destructor
//
// but not more.
//
typedef barn_type::auto_type animal_transport;
//
// Create an empty farm.
//
farm() { }
//
// We need a constructor that can make a new
// farm by cloning a range of animals.
//
farm( animal_iterator begin, animal_iterator end )
:
//
// Objects are always cloned before insertion
// unless we explicitly add a pointer or
// use 'release()'. Therefore we actually
// clone all animals in the range
//
barn( begin, end ) { }
//
// ... so we need some other function too
//
animal_iterator begin()
{
return barn.begin();
}
animal_iterator end()
{
return barn.end();
}
//
// Here it is quite ok to have an 'animal*' argument.
// The smart container will handle all ownership
// issues.
//
void buy_animal( animal* a )
{
barn.push_back( a );
}
//
// The farm can also be in economical trouble and
// therefore be in the need to sell animals.
//
animal_transport sell_animal( animal_iterator to_sell )
{
if( to_sell == end() )
throw farm_trouble();
//
// Here we remove the animal from the barn,
// but the animal is not deleted yet...it's
// up to the buyer to decide what
// to do with it.
//
return barn.release( to_sell );
}
//
// How big a farm do we have?
//
size_type size() const
{
return barn.size();
}
//
// If things are bad, we might choose to sell all animals :-(
//
raii_ptr sell_farm()
{
return barn.release();
}
//
// However, if things are good, we might buy somebody
// else's farm :-)
//
void buy_farm( raii_ptr other )
{
//
// This line inserts all the animals from 'other'
// and is guaranteed either to succeed or to have no
// effect
//
barn.transfer( barn.end(), // insert new animals at the end
*other ); // we want to transfer all animals,
// so we use the whole container as argument
//
// You might think you would have to do
//
// other.release();
//
// but '*other' is empty and can go out of scope as it wants
//
BOOST_ASSERT( other->empty() );
}
}; // class 'farm'.
int main()
{
//
// First we make a farm
//
farm animal_farm;
BOOST_ASSERT( animal_farm.size() == 0u );
animal_farm.buy_animal( new pig("Betty") );
animal_farm.buy_animal( new pig("Benny") );
animal_farm.buy_animal( new pig("Jeltzin") );
animal_farm.buy_animal( new cow("Hanz") );
animal_farm.buy_animal( new cow("Mary") );
animal_farm.buy_animal( new cow("Frederik") );
BOOST_ASSERT( animal_farm.size() == 6u );
//
// Then we make another farm...it will actually contain
// a clone of the other farm.
//
farm new_farm( animal_farm.begin(), animal_farm.end() );
BOOST_ASSERT( new_farm.size() == 6u );
//
// Is it really clones in the new farm?
//
BOOST_ASSERT( new_farm.begin()->name() == "Betty" );
//
// Then we search for an animal, Mary (the Crown Princess of Denmark),
// because we would like to buy her ...
//
typedef farm::animal_iterator iterator;
iterator to_sell;
for( iterator i = animal_farm.begin(),
end = animal_farm.end();
i != end; ++i )
{
if( i->name() == "Mary" )
{
to_sell = i;
break;
}
}
farm::animal_transport mary = animal_farm.sell_animal( to_sell );
if( mary->speak() == muuuh )
//
// Great, Mary is a cow, and she may live longer
//
new_farm.buy_animal( mary.release() );
else
//
// Then the animal would be destroyed (!)
// when we go out of scope.
//
;
//
// Now we can observe some changes to the two farms...
//
BOOST_ASSERT( animal_farm.size() == 5u );
BOOST_ASSERT( new_farm.size() == 7u );
//
// The new farm has however underestimated how much
// it cost to feed Mary and its owner is forced to sell the farm...
//
animal_farm.buy_farm( new_farm.sell_farm() );
BOOST_ASSERT( new_farm.size() == 0u );
BOOST_ASSERT( animal_farm.size() == 12u );
}