diff options
author | Boris Kolpackov <boris@codesynthesis.com> | 2011-08-04 13:29:42 +0200 |
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committer | Boris Kolpackov <boris@codesynthesis.com> | 2011-08-04 13:29:42 +0200 |
commit | 9ac9bb98f307156c02fa19ea747cf5eb1d2dcadf (patch) | |
tree | 8237f586c0198b82c186e7e7700ff9aaf7405bd5 /odb/wrapper-traits.hxx | |
parent | 1d2e161846310145c8bf4343a041818c57ca611e (diff) |
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.
Diffstat (limited to 'odb/wrapper-traits.hxx')
-rw-r--r-- | odb/wrapper-traits.hxx | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/odb/wrapper-traits.hxx b/odb/wrapper-traits.hxx new file mode 100644 index 0000000..fdfb872 --- /dev/null +++ b/odb/wrapper-traits.hxx @@ -0,0 +1,153 @@ +// file : odb/wrapper-traits.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_WRAPPER_TRAITS_HXX +#define ODB_WRAPPER_TRAITS_HXX + +#include <odb/pre.hxx> + +#include <memory> // std::auto_ptr + +#include <odb/nullable.hxx> + +namespace odb +{ + template <typename T> + class wrapper_traits; + + // Sample specialization for raw pointers. It is not enabled by default + // since it makes many assumptions that may not always hold true (such + // as that instances are allocated with new and freed with delete). + // This makes it too dangerous to be enable unconditionally. If you + // need this functionality, you can copy the below code into your + // application. Also consider changing it to only specialize for + // specific types instead of for any pointer (it will almost always + // do the wrong thing for char*). + // +#if 0 + template <typename T> + class wrapper_traits<T*> + { + public: + typedef T wrapped_type; + typedef T* wrapper_type; + + static const bool null_handler = true; + static const bool null_default = false; + + static bool + get_null (const wrapper_type& p) + { + return p == 0; + } + + static void + set_null (wrapper_type& p) + { + delete p; + p = 0; + } + + static const type& + get_ref (const wrapper_type& p) + { + return *p; + } + + static type& + set_ref (wrapper_type& p) + { + if (p == 0) + p = new type; + + return *p; + } + }; +#endif + + // Specialization for std::auto_ptr. + // + template <typename T> + class wrapper_traits< std::auto_ptr<T> > + { + public: + typedef T wrapped_type; + typedef std::auto_ptr<T> wrapper_type; + + static const bool null_handler = true; + static const bool null_default = false; + + static bool + get_null (const wrapper_type& p) + { + return p.get () == 0; + } + + static void + set_null (wrapper_type& p) + { + p.reset (); + } + + static const wrapped_type& + get_ref (const wrapper_type& p) + { + return *p; + } + + static wrapped_type& + set_ref (wrapper_type& p) + { + if (p.get () == 0) + p.reset (new wrapped_type); + + return *p; + } + }; + + // Specialization for odb::nullable. + // + template <typename T> + class wrapper_traits< nullable<T> > + { + public: + typedef T wrapped_type; + typedef nullable<T> wrapper_type; + + static const bool null_handler = true; + static const bool null_default = true; + + static bool + get_null (const wrapper_type& n) + { + return n.null (); + } + + static void + set_null (wrapper_type& n) + { + n.reset (); + } + + static const wrapped_type& + get_ref (const wrapper_type& n) + { + return *n; + } + + static wrapped_type& + set_ref (wrapper_type& n) + { + if (n.null ()) + n = T (); + + return *n; + } + }; +} + +#include <odb/post.hxx> + +#endif // ODB_WRAPPER_TRAITS_HXX |