From fcbdbfa9f6d2e8f1b9874764c40249010095487c Mon Sep 17 00:00:00 2001
From: Christian Engwer <christi@dune-project.org>
Date: Sat, 27 Nov 2010 17:54:16 +0000
Subject: [PATCH] * add null_deleter to shared_ptr to handle stack objects *
add two free functions for convient creation of a shared_ptr from a
stack-allocated object
[[Imported from SVN: r6273]]
---
dune/common/shared_ptr.hh | 68 ++++++++++++++++++++++++++++++
dune/common/test/shared_ptrtest.cc | 20 +++++++++
2 files changed, 88 insertions(+)
diff --git a/dune/common/shared_ptr.hh b/dune/common/shared_ptr.hh
index a3e590e9b..77059386a 100644
--- a/dune/common/shared_ptr.hh
+++ b/dune/common/shared_ptr.hh
@@ -17,6 +17,7 @@
#endif
#include <dune/common/nullptr.hh>
+#include <dune/common/typetraits.hh>
/**
* @file
* @brief This file implements the class shared_ptr (a reference counting
@@ -294,5 +295,72 @@ namespace Dune
/** @} */
#endif // #ifdef SHARED_PTR_NAMESPACE
+ /**
+ @brief implements the Deleter concept of shared_ptr without deleting anything
+ @relates shared_ptr
+
+ If you allocate an object on the stack, but want to pass it to a class or function as a shared_ptr,
+ you can use this deleter to avoid accidential deletion of the stack-allocated object.
+
+ For convinience we provide two free functions to create a shared_ptr from a stack-allocated object
+ (\see stackobject_to_shared_ptr):
+
+ 1) Convert a stack-allocated object to a shared_ptr:
+ @code
+ int i = 10;
+ shared_ptr<int> pi = stackobject_to_shared_ptr(i);
+ @endcode
+ 2) Convert a stack-allocated object to a shared_ptr of a base class
+ @code
+ class A {};
+ class B : public A {};
+
+ ...
+
+ B b;
+ shared_ptr<A> pa = stackobject_to_shared_ptr<A>(b);
+ @endcode
+
+ @tparam T type of the stack-allocated object
+ */
+ template<class T>
+ struct null_deleter
+ {
+ void operator() (T* p) const {}
+ };
+
+ /**
+ @brief Convert a stack-allocated object to a shared_ptr:
+ @relates shared_ptr
+ @code
+ int i = 10;
+ shared_ptr<int> pi = stackobject_to_shared_ptr(i);
+ @endcode
+ */
+ template<typename T>
+ inline shared_ptr<T> stackobject_to_shared_ptr(T & t)
+ {
+ return shared_ptr<T>(&t, null_deleter<T>());
+ }
+
+ /**
+ @brief Convert a stack object to a shared_ptr of a base class
+ @relates shared_ptr
+ @code
+ class A {};
+ class B : public A {};
+
+ ...
+
+ B b;
+ shared_ptr<A> pa = stackobject_to_shared_ptr<A>(b);
+ @endcode
+ */
+ template<typename T, typename T2>
+ inline shared_ptr<T2> stackobject_to_shared_ptr(T & t)
+ {
+ return shared_ptr<T2>(dynamic_cast<T2*>(&t), null_deleter<T2>());
+ }
+
}
#endif
diff --git a/dune/common/test/shared_ptrtest.cc b/dune/common/test/shared_ptrtest.cc
index 86b0473c4..79ea6ab1c 100644
--- a/dune/common/test/shared_ptrtest.cc
+++ b/dune/common/test/shared_ptrtest.cc
@@ -30,6 +30,10 @@ private:
bool& deleted_;
};
+class A {};
+class B : public A {};
+class C : A {};
+
int main(){
using namespace Dune;
int ret=0;
@@ -154,6 +158,22 @@ int main(){
__FILE__<<std::endl;
ret=1;
}
+
+ // test shared_ptr for stack allocation
+ {
+ int i = 10;
+ shared_ptr<int> pi = stackobject_to_shared_ptr(i);
+ }
+
+ // test shared_ptr for stack allocation with down cast
+ {
+ B b;
+ shared_ptr<A> pa = stackobject_to_shared_ptr<A>(b);
+#ifdef SHARED_PTR_COMPILE_FAIL
+ C c;
+ pa = stackobject_to_shared_ptr<A>(c); // A is an inaccessible base of C
+#endif
+ }
}
return (ret);
}
--
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