#if defined( __has_include ) #if __has_include( ) #define USE_FMT #endif #endif #define USE_ASSERT #include constexpr static size_t TabLength = 4; #if defined( USE_FMT ) #include #else #include #endif #include #include #include #include #include #include #if defined( USE_ASSERT ) #include #endif class ItemComponent // 1 common base class with default operations for most functions { public: virtual ~ItemComponent(){} virtual void operation() = 0; virtual bool addChild( std::unique_ptr component ) noexcept { return false; } virtual void removeChild( ItemComponent* component ) noexcept {} virtual ItemComponent* child( int ) const noexcept { return nullptr; } virtual bool isComposite() const noexcept { return false; } virtual bool isWeapon() const noexcept { return false; } virtual const char* name() const noexcept = 0; ItemComponent* parent() const noexcept { return m_Parent; } void setParent( ItemComponent* parent ) noexcept { m_Parent = parent; } private: ItemComponent* m_Parent = nullptr; }; class ItemComposite : public ItemComponent // The composite can have children { public: virtual void operation() override; virtual bool addChild( std::unique_ptr component ) noexcept override; virtual void removeChild( ItemComponent* component ) noexcept override; virtual ItemComponent* child( int ) const noexcept override; virtual bool isComposite() const noexcept override { return true; } private: std::vector> m_Children; }; void ItemComposite::operation() { for( auto& child : m_Children ) { child->operation(); } } bool ItemComposite::addChild( std::unique_ptr component ) noexcept { component->setParent( this ); m_Children.push_back( std::move( component ) ); return true; } void ItemComposite::removeChild( ItemComponent* component ) noexcept { const auto cmp = [&]( const std::unique_ptr& ptr ){ return ptr.get() == component; }; if( auto it = std::find_if( m_Children.begin(), m_Children.end(), cmp ); it != m_Children.end() ) { m_Children.erase( it ); } } ItemComponent* ItemComposite::child( int index ) const noexcept { if( index < 0 || index >= static_cast( m_Children.size() ) ) return nullptr; return m_Children[index].get(); } class Rock : public ItemComponent // Leaf class ( can't have children ) { public: virtual void operation() override { } virtual const char* name() const noexcept override { return "Rock"; } }; class Stick : public ItemComponent // Leaf class { public: virtual void operation() override { } virtual const char* name() const noexcept override { return "Stick"; } }; class Sword : public ItemComponent // Leaf class { public: virtual void operation() override { } virtual bool isWeapon() const noexcept override { return true; } virtual const char* name() const noexcept override { return "Sword"; } }; class Shield : public ItemComponent // Leaf class { public: virtual void operation() override { } virtual bool isWeapon() const noexcept override { return true; } virtual const char* name() const noexcept override { return "Shield"; } }; class Bow : public ItemComponent // Leaf class { public: virtual void operation() override { } virtual bool isWeapon() const noexcept override { return true; } virtual const char* name() const noexcept override { return "Bow"; } }; class Arrow : public ItemComponent // Leaf class { public: virtual void operation() override { } virtual const char* name() const noexcept override { return "Arrow"; } }; class Bag : public ItemComposite // Composite class ( can have children ) { public: virtual void operation() override { ItemComposite::operation(); } virtual const char* name() const noexcept override { return "Bag"; } }; class WeaponBag : public Bag // Composite class, weapon bag disallows adding non weapon types { public: virtual const char* name() const noexcept override { return "WeaponBag"; } virtual bool addChild( std::unique_ptr component ) noexcept override; }; bool WeaponBag::addChild( std::unique_ptr component ) noexcept { if( component->isWeapon() ) { return ItemComposite::addChild( std::move( component ) ); } return false; } // Wrapper around std::make_unique that only allows ItemComponent types template std::unique_ptr make_item_component( Args&&... args ) requires std::is_base_of_v { return std::make_unique( std::forward( args )... ); } class ItemFactory // Item Factory, allows subclassing to allow creating specialized items { public: virtual ~ItemFactory(){} virtual std::unique_ptr create( std::string_view ) const; }; std::unique_ptr ItemFactory::create( std::string_view s ) const { if( s == "Rock" ) return make_item_component(); if( s == "Stick" ) return make_item_component(); if( s == "Sword" ) return make_item_component(); if( s == "Shield" ) return make_item_component(); if( s == "Bow" ) return make_item_component(); if( s == "Arrow" ) return make_item_component(); if( s == "Bag" ) return make_item_component(); if( s == "WeaponBag" ) return make_item_component(); #if defined( USE_ASSERT ) #if defined( USE_FMT ) fmt::print( stderr, "Oops, ItemFactory::create does not know how to construct a '{}'\n", s ); #else std::cerr << "Oops, ItemFactory::create does not know how to construct a '" << s << "'\n"; #endif assert( false ); #endif return {}; } void printInventory( const ItemComponent* root, int depth = 0 ) { if( root ) { #if defined( USE_FMT ) fmt::print( "{}{}\n", std::string( depth * TabLength, ' ' ), root->name() ); #else std::cout << std::string( depth * TabLength, ' ' ) << root->name() << '\n'; #endif int index = 0; const ItemComponent* component = root->child( index ); while( component ) { printInventory( component, depth + 1 ); component = root->child( ++index ); } } } int main() { ItemFactory itemFactory; std::unique_ptr inventory = itemFactory.create( "Bag" ); // Main bag inventory->addChild( itemFactory.create( "Rock" ) ); inventory->addChild( itemFactory.create( "Rock" ) ); inventory->addChild( itemFactory.create( "Stick" ) ); std::unique_ptr weaponBag = itemFactory.create( "WeaponBag" ); // Nested bags weaponBag->addChild( itemFactory.create( "Sword" ) ); weaponBag->addChild( itemFactory.create( "Shield" ) ); weaponBag->addChild( itemFactory.create( "Bow" ) ); if( !weaponBag->addChild( itemFactory.create( "Arrow" ) ) ) // Arrow is not a weapon so addChild will fail { inventory->addChild( itemFactory.create( "Arrow" ) ); // Place it in the inventory instead } inventory->addChild( std::move( weaponBag ) ); for( int i = 0; i < 3; ++i ) inventory->addChild( itemFactory.create( "Arrow" ) ); // inventory->removeChild( inventory->child( 0 ) ); printInventory( inventory.get() ); }

Composite pattern