Implement noinit_allocator_adaptor

doc/core.qbk

@@ -50,6 +50,7 @@ criteria for inclusion is that the utility component be:
 [include is_same.qbk]
 [include lightweight_test.qbk]
 [include no_exceptions_support.qbk]
+[include noinit_adaptor.qbk]
 [include noncopyable.qbk]
 [include null_deleter.qbk]
 [include pointer_traits.qbk]

doc/noinit_adaptor.qbk

@@ -0,0 +1,141 @@
+[/
+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)
+]
+
+[section:noinit_adaptor noinit_adaptor]
+
+[simplesect Authors]
+
+* Glen Fernandes
+
+[endsimplesect]
+
+[section Overview]
+
+The header <boost/core/noinit_adaptor.hpp> provides the class
+template `boost::noinit_adaptor` that converts any allocator into
+one whose `construct(ptr)` performs default initialization via placement new,
+and whose `destroy(ptr)` invokes `value_type` destructor directly.
+
+[endsect]
+
+[section Example]
+
+The following example shows use of this allocator adaptor to achieve default
+initialization of elements of a trivial type, which are later assigned values.
+
+```
+#include <boost/core/noinit_adaptor.hpp>
+#include <numeric>
+
+int main()
+{
+    std::vector<int,
+        boost::noinit_adaptor<std::allocator<int> > > v(5);
+    std::iota(v.begin(), v.end(), 1);
+}
+```
+
+[endsect]
+
+[section Reference]
+
+```
+namespace boost {
+
+template<class A>
+struct noinit_adaptor
+    : A {
+    template<class U>
+    struct rebind {
+        typedef noinit_adaptor<typename std::allocator_traits<A>::template
+            rebind_alloc<U> > other;
+    };
+
+    noinit_adaptor() noexcept;
+
+    template<class U>
+    noinit_adaptor(U&& u) noexcept;
+
+    template<class U>
+    noinit_adaptor(const noinit_adaptor<U>& u) noexcept;
+
+    template<class U>
+    void construct(U* p);
+
+    template<class U, class V, class... Args>
+    void construct(U* p, V&& v, Args&&... args);
+
+    template<class U>
+    void destroy(U* p);
+};
+
+template<class T, class U>
+bool operator==(const noinit_adaptor<T>& lhs,
+    const noinit_adaptor<U>& rhs) noexcept;
+
+template<class T, class U>
+bool operator!=(const noinit_adaptor<T>& lhs,
+    const noinit_adaptor<U>& rhs) noexcept;
+
+} /* boost */
+```
+
+[section Constructors]
+
+[variablelist
+[[`noinit_adaptor() noexcept;`]
+[[variablelist
+[[Effects][Value initializes the A base class.]]]]]
+[[`template<class U> noinit_adaptor(U&& u) noexcept;`]
+[[variablelist
+[[Requires][`A` shall be constructible from `U`.]]
+[[Effects][Initializes the `A` base class with `std::forward<U>(u)`.]]]]]
+[[`template<class U> noinit_adaptor(const noinit_adaptor<U>& u) noexcept;`]
+[[variablelist
+[[Requires][`A` shall be constructible from `U`.]]
+[[Effects][Initializes the `A` base class with
+`static_cast<const U&>(u)`.]]]]]]
+
+[endsect]
+
+[section Member functions]
+
+[variablelist
+[[`template<class U> void construct(U* p);`]
+[[variablelist
+[[Effects][`::new((void*)p) U`.]]]]]
+[[`template<class U, class V, class... Args> void construct(U* p, V&& v,
+Args&&... args);`]
+[[variablelist
+[[Effects][`::new(void*)p) U(std::forward<V>(v),
+std::forward<Args>(args)...)`.]]]]]
+[[`template<class U> void destroy(U* p);`]
+[[variablelist
+[[Effects][`p->~U()`.]]]]]]
+
+[endsect]
+
+[section Operators]
+
+[variablelist
+[[`template<class T, class U> constexpr bool
+operator==(const noinit_adaptor<T>& lhs,
+const noinit_adaptor<U>& rhs) noexcept;`]
+[[variablelist
+[[Returns][`static_cast<const T&>(lhs) == static_cast<const U&>(rhs)`.]]]]]
+[[`template<class T, class U> constexpr bool
+operator!=(const noinit_adaptor<T>& lhs,
+const noinit_adaptor<U>& rhs) noexcept;`]
+[[variablelist
+[[Returns][`!(lhs == rhs)`.]]]]]]
+
+[endsect]
+
+[endsect]
+
+[endsect]

include/boost/core/noinit_adaptor.hpp

@@ -0,0 +1,96 @@
+/*
+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)
+*/
+#ifndef BOOST_CORE_NOINIT_ADAPTOR_HPP
+#define BOOST_CORE_NOINIT_ADAPTOR_HPP
+
+#include <boost/config.hpp>
+#include <memory>
+#include <new>
+#include <utility>
+
+namespace boost {
+
+template<class A>
+struct noinit_adaptor
+    : A {
+    template<class U>
+    struct rebind {
+#if !defined(BOOST_NO_CXX11_ALLOCATOR)
+        typedef noinit_adaptor<typename std::allocator_traits<A>::template
+            rebind_alloc<U> > other;
+#else
+        typedef noinit_adaptor<typename A::template rebind<U>::other> other;
+#endif
+    };
+
+    noinit_adaptor()
+        : A() { }
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+    template<class U>
+    noinit_adaptor(U&& u) BOOST_NOEXCEPT
+        : A(std::forward<U>(u)) { }
+#else
+    template<class U>
+    noinit_adaptor(const U& u) BOOST_NOEXCEPT
+        : A(u) { }
+#endif
+
+    template<class U>
+    noinit_adaptor(const noinit_adaptor<U>& u) BOOST_NOEXCEPT
+        : A(static_cast<const U&>(u)) { }
+
+    template<class U>
+    void construct(U* p) {
+        ::new((void*)p) U;
+    }
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
+    template<class U, class V, class... Args>
+    void construct(U* p, V&& v, Args&&... args) {
+        ::new((void*)p) U(std::forward<V>(v), std::forward<Args>(args)...);
+    }
+#else
+    template<class U, class V>
+    void construct(U* p, V&& v) {
+        ::new((void*)p) U(std::forward<V>(v));
+    }
+#endif
+#else
+    template<class U, class V>
+    void construct(U* p, const V& v) {
+        ::new((void*)p) U(v);
+    }
+#endif
+
+    template<class U>
+    void destroy(U* p) {
+        p->~U();
+    }
+};
+
+template<class T, class U>
+inline bool
+operator==(const noinit_adaptor<T>& lhs,
+    const noinit_adaptor<U>& rhs) BOOST_NOEXCEPT
+{
+    return static_cast<const T&>(lhs) == static_cast<const U&>(rhs);
+}
+
+template<class T, class U>
+inline bool
+operator!=(const noinit_adaptor<T>& lhs,
+    const noinit_adaptor<U>& rhs) BOOST_NOEXCEPT
+{
+    return !(lhs == rhs);
+}
+
+} /* boost */
+
+#endif

test/Jamfile.v2

@@ -137,6 +137,7 @@ run-fail quick_exit_fail.cpp ;
 compile use_default_test.cpp ;
 
 run default_allocator_test.cpp ;
+run noinit_adaptor_test.cpp ;
 
 lib lib_typeid : lib_typeid.cpp : <link>shared:<define>LIB_TYPEID_DYN_LINK=1 ;
 

test/noinit_adaptor_test.cpp

@@ -0,0 +1,107 @@
+/*
+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)
+*/
+#include <boost/core/default_allocator.hpp>
+#include <boost/core/noinit_adaptor.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <vector>
+
+template<class T>
+class creator
+    : public boost::default_allocator<T> {
+public:
+    template<class U>
+    struct rebind {
+        typedef creator<U> other;
+    };
+
+    creator(int* count)
+        : count_(count) { }
+
+    template<class U>
+    creator(const creator<U>& other)
+        : count_(other.count()) { }
+
+    template<class U, class V>
+    void construct(U*, const V&) {
+        ++(*count_);
+    }
+
+    template<class U>
+    void destroy(U*) {
+        --(*count_);
+    }
+
+    int* count() const {
+        return count_;
+    }
+
+private:
+    int* count_;
+};
+
+template<class T, class U>
+inline bool
+operator==(const creator<T>& lhs, const creator<U>& rhs)
+{
+    return lhs.count() == rhs.count();
+}
+
+template<class T, class U>
+inline bool
+operator!=(const creator<T>& lhs, const creator<U>& rhs)
+{
+    return !(lhs == rhs);
+}
+
+class type {
+public:
+    type() { }
+
+    type(int value)
+        : value_(value) { }
+
+    int value() const {
+        return value_;
+    }
+
+private:
+    int value_;
+};
+
+int main()
+{
+    {
+        int c = 0;
+        std::vector<int, boost::noinit_adaptor<creator<int> > > v(&c);
+        BOOST_TEST(c == 0);
+        v.push_back(1);
+        BOOST_TEST(v.front() == 1);
+        v.push_back(2);
+        BOOST_TEST(c == 0);
+        v.clear();
+        BOOST_TEST(c == 0);
+        v.resize(5);
+        BOOST_TEST(c == 0);
+        v.front() = 1;
+    }
+    {
+        int c = 0;
+        std::vector<type, boost::noinit_adaptor<creator<type> > > v(&c);
+        BOOST_TEST(c == 0);
+        v.push_back(1);
+        BOOST_TEST(v.front().value() == 1);
+        v.push_back(2);
+        BOOST_TEST(c == 0);
+        v.clear();
+        BOOST_TEST(c == 0);
+        v.resize(5);
+        BOOST_TEST(c == 0);
+        v.front() = 1;
+    }
+    return boost::report_errors();
+}