From 9ac9bb98f307156c02fa19ea747cf5eb1d2dcadf Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 4 Aug 2011 13:29:42 +0200
Subject: Add support for value wrappers

Wrapper is a class that wraps another type. Examples of wrappers are
various smart pointers, holders, etc. A wrapper can be transparent or
it can handle the NULL semantics.

The new odb::nullable class template is a NULL wrapper that helps
to add the NULL semantics to a value type.

New test: common/wrapper.
---
 odb/nullable.hxx | 199 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 199 insertions(+)
 create mode 100644 odb/nullable.hxx

(limited to 'odb/nullable.hxx')

diff --git a/odb/nullable.hxx b/odb/nullable.hxx
new file mode 100644
index 0000000..4b33564
--- /dev/null
+++ b/odb/nullable.hxx
@@ -0,0 +1,199 @@
+// file      : odb/nullable.hxx
+// author    : Boris Kolpackov <boris@codesynthesis.com>
+// copyright : Copyright (c) 2009-2011 Code Synthesis Tools CC
+// license   : GNU GPL v2; see accompanying LICENSE file
+
+#ifndef ODB_NULLABLE_HXX
+#define ODB_NULLABLE_HXX
+
+#include <odb/pre.hxx>
+
+namespace odb
+{
+  template <typename T>
+  class nullable
+  {
+  public:
+    typedef T value_type;
+
+    nullable ();
+    nullable (const T&);
+    nullable (const nullable&);
+    template <typename Y> explicit nullable (const nullable<Y>&);
+
+    nullable& operator= (const T&);
+    nullable& operator= (const nullable&);
+    template <typename Y> nullable& operator= (const nullable<Y>&);
+
+    void swap (nullable&);
+
+    bool null () const;
+
+    T&       get ();
+    const T& get () const;
+
+    T*       operator-> ();
+    const T* operator-> () const;
+
+    T&       operator* ();
+    const T& operator* () const;
+
+    typedef void (nullable::*bool_convertible) ();
+    operator bool_convertible () const
+    {
+      return null_ ? 0 : &nullable<T>::true_value;
+    }
+
+    void reset ();
+
+  private:
+    void true_value () {};
+
+    T value_;
+    bool null_;
+  };
+
+  namespace core
+  {
+    using odb::nullable;
+  }
+
+  template <typename T>
+  inline nullable<T>::
+  nullable ()
+      : null_ (true)
+  {
+  }
+
+  template <typename T>
+  inline nullable<T>::
+  nullable (const T& v)
+      : value_ (v), null_ (false)
+  {
+  }
+
+  template <typename T>
+  inline nullable<T>::
+  nullable (const nullable& y)
+      : value_ (y.value_), null_ (y.null_)
+  {
+  }
+
+  template <typename T>
+  template <typename Y>
+  inline nullable<T>::
+  nullable (const nullable<Y>& y)
+      : value_ (y.value_), null_ (y.null_)
+  {
+  }
+
+  template <typename T>
+  inline nullable<T>& nullable<T>::
+  operator= (const T& v)
+  {
+    value_ = v;
+    null_ = false;
+    return *this;
+  }
+
+  template <typename T>
+  inline nullable<T>& nullable<T>::
+  operator= (const nullable& y)
+  {
+    if (this != &y)
+    {
+      if (!y.null_)
+        value_ = y.value_;
+
+      null_ = y.null_;
+    }
+
+    return *this;
+  }
+
+  template <typename T>
+  template <typename Y>
+  inline nullable<T>& nullable<T>::
+  operator= (const nullable<Y>& y)
+  {
+    if (!y.null_)
+      value_ = y.value_;
+
+    null_ = y.null_;
+    return *this;
+  }
+
+  template <typename T>
+  inline void nullable<T>::
+  swap (nullable& y)
+  {
+    T v (value_);
+    bool n (null_);
+
+    value_ = y.value_;
+    null_ = y.null_;
+
+    y.value_ = v;
+    y.null_ = n;
+  }
+
+  template <typename T>
+  inline bool nullable<T>::
+  null () const
+  {
+    return null_;
+  }
+
+  template <typename T>
+  inline T& nullable<T>::
+  get ()
+  {
+    return value_;
+  }
+
+  template <typename T>
+  inline const T& nullable<T>::
+  get () const
+  {
+    return value_;
+  }
+
+  template <typename T>
+  inline T* nullable<T>::
+  operator-> ()
+  {
+    return null_ ? 0 : &value_;
+  }
+
+  template <typename T>
+  inline const T* nullable<T>::
+  operator-> () const
+  {
+    return null_ ? 0 : &value_;
+  }
+
+  template <typename T>
+  inline T& nullable<T>::
+  operator* ()
+  {
+    return value_;
+  }
+
+  template <typename T>
+  inline const T& nullable<T>::
+  operator* () const
+  {
+    return value_;
+  }
+
+  template <typename T>
+  inline void nullable<T>::
+  reset ()
+  {
+    null_ = true;
+  }
+}
+
+#include <odb/post.hxx>
+
+#endif // ODB_NULLABLE_HXX
-- 
cgit v1.1