Added boost::initialized<T> as was agreed at http://lists.boost.org/Archives/boost/2010/04/164916.php -- see #3472

[SVN r61883]

initialized_test.cpp

@@ -0,0 +1,116 @@
+// Copyright 2010, Niels Dekker.
+//
+// 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)
+//
+// Test program for boost::initialized<T>.
+//
+// 2 May 2010 (Created) Niels Dekker
+
+#include <boost/utility/value_init.hpp>
+#include <boost/detail/lightweight_test.hpp>
+
+#include <string>
+
+namespace
+{
+  // Typical use case for boost::initialized<T>: A generic class that 
+  // holds a value of type T, which must be initialized by either 
+  // value-initialization or direct-initialization.
+  template <class T> class key_value_pair
+  {
+    std::string m_key;
+    boost::initialized<T> m_value;
+  public:
+ 
+    // Value-initializes the object held by m_value.
+    key_value_pair() { }
+
+    // Value-initializes the object held by m_value.
+    explicit key_value_pair(const std::string& key)
+    :
+    m_key(key)
+    {
+    }
+
+    // Direct-initializes the object held by m_value.
+    key_value_pair(const std::string& key, const T& value)
+    :
+    m_key(key), m_value(value)
+    {
+    }
+
+    const T& get_value() const
+    {
+      return m_value;
+    }
+  };
+
+
+  // Tells whether the argument is value-initialized.
+  bool is_value_initialized(const int& arg)
+  {
+    return arg == 0;
+  }
+
+
+  // Tells whether the argument is value-initialized.
+  bool is_value_initialized(const std::string& arg)
+  {
+    return arg.empty();
+  }
+
+  struct foo
+  {
+    int data;
+  };
+
+  bool operator==(const foo& lhs, const foo& rhs)
+  {
+    return lhs.data == rhs.data;
+  }
+
+
+  // Tells whether the argument is value-initialized.
+  bool is_value_initialized(const foo& arg)
+  {
+    return arg.data == 0;
+  }
+
+
+  template <class T>
+  void test_key_value_pair(const T& magic_value)
+  {
+    // The value component of a default key_value_pair must be value-initialized.
+    key_value_pair<T> default_key_value_pair;
+    BOOST_TEST( is_value_initialized(default_key_value_pair.get_value() ) );
+
+    // The value component of a key_value_pair that only has its key explicitly specified
+    // must also be value-initialized.
+    BOOST_TEST( is_value_initialized(key_value_pair<T>("key").get_value()) );
+
+    // However, the value component of the following key_value_pair must be 
+    // "magic_value", as it must be direct-initialized.
+    BOOST_TEST( key_value_pair<T>("key", magic_value).get_value() == magic_value );
+  }
+}
+
+
+// Tests boost::initialize for a fundamental type, a type with a
+// user-defined constructor, and a user-defined type without 
+// a user-defined constructor.
+int main()
+{
+
+  const int magic_number = 42;
+  test_key_value_pair(magic_number);
+
+  const std::string magic_string = "magic value";
+  test_key_value_pair(magic_string);
+
+  const foo magic_foo = { 42 };
+  test_key_value_pair(magic_foo);
+
+  return boost::report_errors();
+}