-[library Boost.Functional/Factory
- [quickbook 1.3]
- [version 1.0]
- [authors [Schwinger, Tobias]]
- [copyright 2007 2008 Tobias Schwinger]
- [license
- Distributed under 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])
- ]
- [purpose Function object templates for object creation.]
- [category higher-order]
- [category generic]
- [last-revision $Date: 2008/11/01 21:44:52 $]
+[/
+Copyright 2007,2008 Tobias Schwinger
+
+Copyright 2019 Glen Joseph Fernandes
+(glenjofe@gmail.com)
+
+Distributed under the Boost Software License, Version 1.0.
+(http://www.boost.org/LICENSE_1_0.txt)
]
-[def __boost_bind__ [@http://www.boost.org/libs/bind/bind.html Boost.Bind]]
-[def __boost__bind__ [@http://www.boost.org/libs/bind/bind.html `boost::bind`]]
+[library Boost.Functional/Factory
+[quickbook 1.5]
+[version 1.0]
+[authors [Schwinger, Tobias], [Fernandes, Glen]]
+[copyright 2007 2008 Tobias Schwinger]
+[copyright 2019 Glen Joseph Fernandes]
+[license Distributed under the Boost Software License, Version 1.0.]
+[purpose Function object templates for object creation.]
+[category higher-order]
+[category generic]]
+
+[def __boost__bind__
+[@http://www.boost.org/libs/bind/bind.html `boost::bind`]]
+
+[def __boost__forward_adapter__
+[@http://www.boost.org/libs/functional/forward/doc/index.html
+`boost::forward_adapter`]]
-[def __boost__forward_adapter__ [@http://www.boost.org/libs/functional/forward/doc/index.html `boost::forward_adapter`]]
-[def __fusion_functional_adapters__ [@http://www.boost.org/libs/fusion/doc/html/functional.html Fusion Functional Adapters]]
+[def __boost_function__
+[@http://www.boost.org/doc/html/function.html Boost.Function]]
-[def __boost_function__ [@http://www.boost.org/doc/html/function.html Boost.Function]]
-[def __boost__function__ [@http://www.boost.org/doc/html/function.html `boost::function`]]
+[def __smart_pointer__
+[@http://www.boost.org/libs/smart_ptr/index.html Smart Pointer]]
-[def __smart_pointer__ [@http://www.boost.org/libs/smart_ptr/index.html Smart Pointer]]
-[def __smart_pointers__ [@http://www.boost.org/libs/smart_ptr/index.html Smart Pointers]]
-[def __boost__shared_ptr__ [@http://www.boost.org/libs/smart_ptr/shared_ptr.htm `boost::shared_ptr`]]
+[def __smart_pointers__
+[@http://www.boost.org/libs/smart_ptr/index.html Smart Pointers]]
-[def __std__map__ [@http://www.sgi.com/tech/stl/map.html `std::map`]]
-[def __std__string__ [@http://www.sgi.com/tech/stl/string.html `std::string`]]
-[def __allocator__ [@http://www.sgi.com/tech/stl/concepts/allocator.html Allocator]]
-[def __std_allocator__ [@http://www.sgi.com/tech/stl/concepts/allocator.html Allocator]]
-[def __std_allocators__ [@http://www.sgi.com/tech/stl/concepts/allocator.html Allocators]]
+[def __boost__shared_ptr__
+[@http://www.boost.org/libs/smart_ptr/shared_ptr.htm `boost::shared_ptr`]]
-[def __boost__ptr_map__ [@http://www.boost.org/libs/ptr_container/doc/ptr_map.html `boost::ptr_map`]]
+[def __allocator__ [@https://www.boost.org/sgi/stl/Allocators.html Allocator]]
+
+[def __std_allocators__
+[@https://www.boost.org/sgi/stl/Allocators.html Allocators]]
[def __boost__factory__ `boost::factory`]
+
[def __boost__value_factory__ `boost::value_factory`]
-[def __factory__ `factory`]
[def __value_factory__ `value_factory`]
-
[section Brief Description]
-The template __boost__factory__ lets you encapsulate a `new` expression
-as a function object, __boost__value_factory__ encapsulates a constructor
-invocation without `new`.
+The template __boost__factory__ lets you encapsulate a `new` expression as a
+function object, __boost__value_factory__ encapsulates a constructor invocation
+without `new`.
- __boost__factory__<T*>()(arg1,arg2,arg3)
- // same as new T(arg1,arg2,arg3)
+```
+__boost__factory__<T*>()(arg1,arg2,arg3)
+// same as new T(arg1,arg2,arg3)
- __boost__value_factory__<T>()(arg1,arg2,arg3)
- // same as T(arg1,arg2,arg3)
+__boost__value_factory__<T>()(arg1,arg2,arg3)
+// same as T(arg1,arg2,arg3)
+```
-For technical reasons the arguments to the function objects have to be
-LValues. A factory that also accepts RValues can be composed using the
-__boost__forward_adapter__ or __boost__bind__.
+Before C++11 the arguments to the function objects have to be LValues. A
+factory that also accepts RValues can be composed using the
+__boost__forward_adapter__ or __boost__bind__. In C++11 or higher the
+arguments can be LValues or RValues.
[endsect]
an interface of one or more methods that construct objects conforming to known
interfaces.
- // assuming a_concrete_class and another_concrete_class are derived
- // from an_abstract_class
-
- class a_factory
- {
- public:
- virtual an_abstract_class* create() const = 0;
- virtual ~a_factory() { }
- };
-
- class a_concrete_factory : public a_factory
- {
- public:
- virtual an_abstract_class* create() const
- {
- return new a_concrete_class();
- }
- };
-
- class another_concrete_factory : public a_factory
- {
- public:
- virtual an_abstract_class* create() const
- {
- return new another_concrete_class();
- }
- };
+```
+// assuming a_concrete_class and another_concrete_class are derived
+// from an_abstract_class
- // [...]
+struct a_factory {
+ virtual an_abstract_class* create() const = 0;
+ virtual ~a_factory() { }
+};
- int main()
- {
- __boost__ptr_map__<__std__string__,a_factory> factories;
+struct a_concrete_factory
+ : a_factory {
+ an_abstract_class* create() const {
+ return new a_concrete_class();
+ }
+};
- // [...]
+struct another_concrete_factory
+ : a_factory {
+ an_abstract_class* create() const {
+ return new another_concrete_class();
+ }
+};
- factories.insert("a_name",std::auto_ptr<a_factory>(
- new a_concrete_factory));
- factories.insert("another_name",std::auto_ptr<a_factory>(
- new another_concrete_factory));
+// [...]
- // [...]
+int main()
+{
+ boost::ptr_map<std::string, a_factory> factories;
- std::auto_ptr<an_abstract_class> x(factories.at(some_name).create());
+ // [...]
- // [...]
- }
+ factories.insert("a_name",
+ std::unique_ptr<a_factory>(new a_concrete_factory));
+ factories.insert("another_name",
+ std::unique_ptr<a_factory>(new another_concrete_factory));
+
+ // [...]
+
+ std::unique_ptr<an_abstract_class> x(factories.at(some_name).create());
+
+ // [...]
+}
+```
-This approach has several drawbacks. The most obvious one is that there is
-lots of boilerplate code. In other words there is too much code to express
-a rather simple intention. We could use templates to get rid of some of it
-but the approach remains inflexible:
+This approach has several drawbacks. The most obvious one is that there is lots
+of boilerplate code. In other words there is too much code to express a rather
+simple intention. We could use templates to get rid of some of it but the
+approach remains inflexible:
-* We may want a factory that takes some arguments that are forwarded to
- the constructor,
+* We may want a factory that takes some arguments that are forwarded to the
+constructor,
* we will probably want to use smart pointers,
-* we may want several member functions to create different kinds of
- objects,
+* we may want several member functions to create different kinds of objects,
* we might not necessarily need a polymorphic base class for the objects,
-* as we will see, we do not need a factory base class at all,
-* we might want to just call the constructor - without `new` to create
- an object on the stack, and
+* as we will see, we do not need a factory base class at all,
+* we might want to just call the constructor - without `new` to create an
+object on the stack, and
* finally we might want to use customized memory management.
Experience has shown that using function objects and generic Boost components
for their composition, Design Patterns that describe callback mechanisms
(typically requiring a high percentage of boilerplate code with pure Object
Oriented methodology) become implementable with just few code lines and without
-extra classes.
+extra classes.
Factories are callback mechanisms for constructors, so we provide two class
templates, __boost__value_factory__ and __boost__factory__, that encapsulate
object construction via direct application of the constructor and the `new`
-operator, respectively.
+operator, respectively.
We let the function objects forward their arguments to the construction
expressions they encapsulate. Over this __boost__factory__ optionally allows
Compile-time polymorphism can be used where appropriate,
- template< class T >
- void do_something()
- {
- // [...]
- T x = T(a,b);
+```
+template<class T>
+void do_something()
+{
+ // [...]
+ T x = T(a, b);
- // for conceptually similar objects x we neither need virtual
- // functions nor a common base class in this context.
- // [...]
- }
+ // for conceptually similar objects x we neither need virtual
+ // functions nor a common base class in this context.
+ // [...]
+}
+```
Now, to allow inhomogeneous signatures for the constructors of the types passed
-in for `T` we can use __value_factory__ and __boost__bind__ to normalize between
-them.
-
- template< class ValueFactory >
- void do_something(ValueFactory make_obj = ValueFactory())
- {
- // [...]
- typename ValueFactory::result_type x = make_obj(a,b);
-
- // for conceptually similar objects x we neither need virtual
- // functions nor a common base class in this context.
- // [...]
- }
+in for `T` we can use __value_factory__ and __boost__bind__ to normalize
+between them.
- int main()
- {
- // [...]
+```
+template<class ValueFactory>
+void do_something(ValueFactory make_obj = ValueFactory())
+{
+ // [...]
+ typename ValueFactory::result_type x = make_obj(a, b);
- do_something(__boost__value_factory__<X>());
- do_something(boost::bind(__boost__value_factory__<Y>(),_1,5,_2));
- // construct X(a,b) and Y(a,5,b), respectively.
+ // for conceptually similar objects x we neither need virtual
+ // functions nor a common base class in this context.
+ // [...]
+}
- // [...]
- }
+int main()
+{
+ // [...]
-Maybe we want our objects to outlive the function's scope, in this case we
-have to use dynamic allocation;
-
- template< class Factory >
- whatever do_something(Factory new_obj = Factory())
- {
- typename Factory::result_type ptr = new_obj(a,b);
-
- // again, no common base class or virtual functions needed,
- // we could enforce a polymorphic base by writing e.g.
- // boost::shared_ptr<base>
- // instead of
- // typename Factory::result_type
- // above.
- // Note that we are also free to have the type erasure happen
- // somewhere else (e.g. in the constructor of this function's
- // result type).
-
- // [...]
- }
+ do_something(boost::value_factory<X>());
+ do_something(boost::bind(boost::value_factory<Y>(), _1, 5, _2));
+ // construct X(a, b) and Y(a, 5, b), respectively.
- // [... call do_something like above but with __factory__ instead
- // of __value_factory__]
+ // [...]
+}
+```
+
+Maybe we want our objects to outlive the function's scope, in this case we have
+to use dynamic allocation;
+
+```
+template<class Factory>
+whatever do_something(Factory new_obj = Factory())
+{
+ typename Factory::result_type ptr = new_obj(a, b);
+
+ // again, no common base class or virtual functions needed,
+ // we could enforce a polymorphic base by writing e.g.
+ // boost::shared_ptr<base>
+ // instead of
+ // typename Factory::result_type
+ // above.
+ // Note that we are also free to have the type erasure happen
+ // somewhere else (e.g. in the constructor of this function's
+ // result type).
-Although we might have created polymorphic objects in the previous example,
-we have used compile time polymorphism for the factory. If we want to erase
-the type of the factory and thus allow polymorphism at run time, we can
-use __boost_function__ to do so. The first example can be rewritten as
-follows.
+ // [...]
+}
- typedef boost::function< an_abstract_class*() > a_factory;
+// [... call do_something like above but with boost::factory instead
+// of boost::value_factory]
+```
- // [...]
+Although we might have created polymorphic objects in the previous example, we
+have used compile time polymorphism for the factory. If we want to erase the
+type of the factory and thus allow polymorphism at run time, we can use
+__boost_function__ to do so. The first example can be rewritten as follows.
+
+```
+typedef boost::function<an_abstract_class*()> a_factory;
- int main()
- {
- __std__map__<__std__string__,a_factory> factories;
+// [...]
- // [...]
+int main()
+{
+ std::map<std::string, a_factory> factories;
+
+ // [...]
- factories["a_name"] = __boost__factory__<a_concrete_class*>();
- factories["another_name"] =
- __boost__factory__<another_concrete_class*>();
+ factories["a_name"] = boost::factory<a_concrete_class*>();
+ factories["another_name"] = boost::factory<another_concrete_class*>();
- // [...]
- }
+ // [...]
+}
+```
Of course we can just as easy create factories that take arguments and/or
return __smart_pointers__.
[endsect]
-
[section:reference Reference]
-
[section value_factory]
[heading Description]
Function object template that invokes the constructor of the type `T`.
[heading Header]
- #include <boost/functional/value_factory.hpp>
+
+```
+#include <boost/functional/value_factory.hpp>
+```
[heading Synopsis]
- namespace boost
- {
- template< typename T >
- class value_factory;
- }
+```
+namespace boost {
+
+template<class T>
+class value_factory;
+
+} // boost
+```
[variablelist Notation
- [[`T`] [an arbitrary type with at least one public constructor]]
- [[`a0`...`aN`] [argument LValues to a constructor of `T`]]
- [[`F`] [the type `value_factory<F>`]]
- [[`f`] [an instance object of `F`]]
-]
+[[`T`][an arbitrary type with at least one public constructor]]
+[[`a0`...`aN`][argument values to a constructor of `T`]]
+[[`F`][the type `value_factory<F>`]]
+[[`f`][an instance object of `F`]]]
[heading Expression Semantics]
[table
- [[Expression] [Semantics]]
- [[`F()`] [creates an object of type `F`.]]
- [[`F(f)`] [creates an object of type `F`.]]
- [[`f(a0`...`aN)`] [returns `T(a0`...`aN)`.]]
- [[`F::result_type`] [is the type `T`.]]
-]
+[[Expression][Semantics]]
+[[`F()`][creates an object of type `F`.]]
+[[`F(f)`][creates an object of type `F`.]]
+[[`f(a0`...`aN)`][returns `T(a0`...`aN)`.]]
+[[`F::result_type`][is the type `T`.]]]
[heading Limits]
-The macro BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY can be defined to set the
-maximum arity. It defaults to 10.
+Before C++11, the maximum number of arguments supported is 10. Since C++11 an
+arbitrary number of arguments is supported.
[endsect]
-
[section factory]
[heading Description]
-Function object template that dynamically constructs a pointee object for
-the type of pointer given as template argument. Smart pointers may be used
-for the template argument, given that `boost::pointee<Pointer>::type` yields
+Function object template that dynamically constructs a pointee object for the
+type of pointer given as template argument. Smart pointers may be used for the
+template argument, given that `pointer_traits<Pointer>::element_type` yields
the pointee type.
-If an __allocator__ is given, it is used for memory allocation and the
-placement form of the `new` operator is used to construct the object.
-A function object that calls the destructor and deallocates the memory
-with a copy of the Allocator is used for the second constructor argument
-of `Pointer` (thus it must be a __smart_pointer__ that provides a suitable
-constructor, such as __boost__shared_ptr__).
+If an __allocator__ is given, it is used for memory allocation and the
+placement form of the `new` operator is used to construct the object. A
+function object that calls the destructor and deallocates the memory with a
+copy of the Allocator is used for the second constructor argument of `Pointer`
+(thus it must be a __smart_pointer__ that provides a suitable constructor,
+such as __boost__shared_ptr__).
-If a third template argument is `factory_passes_alloc_to_smart_pointer`,
-the allocator itself is used for the third constructor argument of `Pointer`
+If a third template argument is `factory_passes_alloc_to_smart_pointer`, the
+allocator itself is used for the third constructor argument of `Pointer`
(__boost__shared_ptr__ then uses the allocator to manage the memory of its
separately allocated reference counter).
[heading Header]
- #include <boost/functional/factory.hpp>
+
+```
+#include <boost/functional/factory.hpp>
+```
[heading Synopsis]
- namespace boost
- {
- enum factory_alloc_propagation
- {
- factory_alloc_for_pointee_and_deleter,
- factory_passes_alloc_to_smart_pointer
- };
-
- template< typename Pointer,
- class Allocator = void,
- factory_alloc_propagation AllocProp =
- factory_alloc_for_pointee_and_deleter >
- class factory;
- }
+```
+namespace boost {
+
+enum factory_alloc_propagation {
+ factory_alloc_for_pointee_and_deleter,
+ factory_passes_alloc_to_smart_pointer
+};
+
+template<class Pointer,
+ class Allocator = void,
+ factory_alloc_propagation Policy = factory_alloc_for_pointee_and_deleter>
+class factory;
+
+} // boost
+```
[variablelist Notation
- [[`T`] [an arbitrary type with at least one public constructor]]
- [[`P`] [pointer or smart pointer to `T`]]
- [[`a0`...`aN`] [argument LValues to a constructor of `T`]]
- [[`F`] [the type `factory<P>`]]
- [[`f`] [an instance object of `F`]]
-]
+[[`T`][an arbitrary type with at least one public constructor]]
+[[`P`][pointer or smart pointer to `T`]]
+[[`a0`...`aN`][argument values to a constructor of `T`]]
+[[`F`][the type `factory<P>`]]
+[[`f`][an instance object of `F`]]]
[heading Expression Semantics]
[table
- [[Expression] [Semantics]]
- [[`F()`] [creates an object of type `F`.]]
- [[`F(f)`] [creates an object of type `F`.]]
- [[`f(a0`...`aN)`] [dynamically creates an object of type `T` using
- `a0`...`aN` as arguments for the constructor invocation.]]
- [[`F::result_type`] [is the type `P` with top-level cv-qualifiers removed.]]
-]
+[[Expression][Semantics]]
+[[`F()`][creates an object of type `F`.]]
+[[`F(f)`][creates an object of type `F`.]]
+[[`f(a0`...`aN)`]
+[dynamically creates an object of type `T` using `a0`...`aN` as arguments for
+the constructor invocation.]]
+[[`F::result_type`][is the type `P` with top-level cv-qualifiers removed.]]]
[heading Limits]
-The macro BOOST_FUNCTIONAL_FACTORY_MAX_ARITY can be defined to set the
-maximum arity. It defaults to 10.
+Before C++11, the maximum number of arguments supported is 10. Since C++11 an
+arbitrary number of arguments is supported.
[endsect]
[section Changes]
+[heading Boost 1.72.0]
+
+Glen Fernandes rewrote the implementations of `factory` and `value_factory` to
+provide the following features:
+
+* Support r-value arguments when available
+* Support arbitrary number of arguments via variadic templates when available
+* Support allocators that are final
+* Support allocators that use fancy pointers
+* Support for disabled exceptions (`BOOST_NO_EXCEPTIONS`)
+* Improved compilation times
+
+The following features have been removed:
+
+* Increasing limits for C++03 compilers through
+ `BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY`
+* Using `boost::none_t` in place of `void` through
+ `BOOST_FUNCTIONAL_FACTORY_SUPPORT_NONE_T`
+
[heading Boost 1.58.0]
-In order to remove the dependency on Boost.Optional, the default parameter
-for allocators has been changed from `boost::none_t` to `void`.
-If you have code that has stopped working because it uses `boost::none_t`,
-a quick fix is to define `BOOST_FUNCTIONAL_FACTORY_SUPPORT_NONE_T`, which will
-restore support, but this will be removed in a future release.
-It should be be relatively easy to fix this properly.
+In order to remove the dependency on Boost.Optional, the default parameter for
+allocators has been changed from `boost::none_t` to `void`. If you have code
+that has stopped working because it uses `boost::none_t`, a quick fix is to
+define `BOOST_FUNCTIONAL_FACTORY_SUPPORT_NONE_T`, which will restore support,
+but this will be removed in a future release. It should be be relatively easy
+to fix this properly.
[endsect]
[section Acknowledgements]
-Eric Niebler requested a function to invoke a type's constructor (with the
+Tobias Schwinger for creating this library.
+
+Eric Niebler requested a function to invoke a type's constructor (with the
arguments supplied as a Tuple) as a Fusion feature. These Factory utilities are
a factored-out generalization of this idea.
Joel de Guzman's documentation style was copied from Fusion.
-Further, I want to thank Peter Dimov for sharing his insights on language
-details and their evolution.
+Peter Dimov for sharing his insights on language details and their evolution.
[endsect]
[section References]
# [@http://en.wikipedia.org/wiki/Design_Patterns Design Patterns],
- Gamma et al. - Addison Wesley Publishing, 1995
+Gamma et al. - Addison Wesley Publishing, 1995
-# [@http://www.sgi.com/tech/stl/ Standard Template Library Programmer's Guide],
- Hewlett-Packard Company, 1994
+# [@https://boost.org/sgi/stl/ Standard Template Library Programmer's Guide],
+Hewlett-Packard Company, 1994
-# [@http://www.boost.org/libs/bind/bind.html Boost.Bind],
- Peter Dimov, 2001-2005
+# [@http://www.boost.org/libs/bind/bind.html Boost.Bind],
+Peter Dimov, 2001-2005
# [@http://www.boost.org/doc/html/function.html Boost.Function],
- Douglas Gregor, 2001-2004
+Douglas Gregor, 2001-2004
[endsect]
-
-
projects / platform / upstream / boost.git / blobdiff