functional-factory.md

Boost.Functional/Factory

• lib: boost/libs/functional/factory
• repo: boostorg/functional
• commit: 1706cb59, 2017-02-03

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Factory Wrappers

Header <boost/functional/factory.hpp> and <boost/functional/value_factory.hpp>

enum factory_alloc_propagation {
  factory_alloc_for_pointee_and_deleter,  factory_passes_alloc_to_smart_pointer
};

template<typename Pointer, typename Allocator=void,
  factory_alloc_propagation AP=factory_alloc_for_pointee_and_deleter>
class factory : allocator_type { // when not 'void'
public:
  using result_type = remove_cv<Pointer>::type;
  using value_type = boost::pointee<result_type>::type;
  using allocator_type = Allocator::rebind<value_type>::other; // when not 'void'
  
  factory(Allocator const& a = Allocator());
  template<typename ...T> result_type operator()(T &... a) const {
    return result_type(new value_type(a...)); // for 'Allocator' is 'void'
    value_type* ptr = new (allocate(1)) value_type(a...);
    return result_type(ptr,
      /*deleter*/[](value_type* ptr){ ptr && ptr->~value_type(); this->deallocate(ptr, 1); },
      /*allocator*/ *this); // when AP == factory_alloc_for_pointee_and_deleter
  }
};

template<typename T>
class value_factory {
public:
  using result_type = T;
  value_factory();
  template<typename ...T> result_type operator()(T &... a) const { return T(a...); }
};

• Factories wrapps object construction expressions, which are not bindable.
• factory supports T*, as well as smart pointer types.
• factory used with Allocator, can be used with smart pointers like smart_ptr, which accepting a deleter and an allocator.

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Dependency

Boost.Config

• <boost/config.hpp>

Boost.Core

• <boost/get_pointer.hpp>

Boost.Iterator

• <boost/pointee.hpp>

Boost.TypeTraits

• <boost/type_traits/remove_cv.hpp>

Boost.Preprocessor

• <boost/preprocessor/iteration/iterate.hpp>
• <boost/preprocessor/repetition/enum_params.hpp>, <boost/preprocessor/repetition/enum_binary_params.hpp>

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Standard Facilities

Language: lambda expression (C++11)