owned_pointer

This is test utility for dependency injection with std::unique_ptr smart pointer, written in C++ 11. Class csp::owned_pointer acts as facade to std::unique_ptr and has semantics and syntax of smart pointer. Class csp::owned_pointer is not intended to be used in production code. It is best to use this class with google mock, to inject mock to cut(class under test) by std::unique_ptr and have reference to this mock in test suite.

Semantics and syntax of csp::owned_pointer

Example of test classes:

struct T
{
  T(int px = 0, int py = 0, int pz = 0) : x(px), y(py), z(pz){}
  int x, y, z;
};

struct X
{
  X(std::unique_ptr<T> m) : u(std::move(m)){}
  std::unique_ptr<T> u;
};

Using csp::owned_pointer:

csp::owned_pointer<T> p = csp::make_owned<T>(1, 2, 3);
X x{p.unique_ptr()}; //after this point owned_pointer is not owner of memory

x.u->x = 10;

assert(x.u->x == p->x);

Class csp::owned_pointer is not owner of memory after unique_ptr() invokation.

std::unique_ptr<T> u;
{
  auto p = csp::make_owned<T>();
  u = p.unique_ptr();
}
auto naked_ptr = u.get(); //u is still valid after destruction of p

If class which is pointed by csp::owned_pointer has virtual dtor and was created by csp::make_owned, csp::owned_pointer is able to detect that std::unique_ptr deleted resource. If class has no virtual dtor invoking get(), operator->() or operator*() after std::unique_ptr deleted resource is undefined.

struct D
{
  int x = 0;
  virtual ~D() = default;
};

try
{
  auto p = csp::make_owned<D>();
  { auto u = p.unique_ptr(); } //nested scope, u deleted
  p->x = 10; // this throws, for T type this would be undefined
}
catch(const csp::ptr_was_alredy_deleted&)
{}

Smart pointer csp::owned_pointer behaves like std::shared_ptr if member function unique_ptr() was not invoked. This means that it will destroy allocated memory, if std::unique_ptr was not acquired.

You can invoke unique_ptr() only once if csp::owned_pointer was in charge of valid memory or infinite number of times if csp::owned_pointer was pointing to nullptr.

try
{
  auto p = csp::make_owned<T>();
  auto u = p.unique_ptr();

  if(not p.expired()) //check if u deleted pointer
    auto v = p.unique_ptr(); //this throws
}
catch(const csp::unique_ptr_already_acquired&)
{}

You can also create csp::owned_pointer from valid std::unique_ptr. Please note that detecting of std::unique_ptr deletion will not work.

auto u = std::make_unique<T>(1, 2, 3);
csp::owned_pointer<T> p{csp::link(u)};

assert(p.get() == u.get());
auto v = p.unique_ptr(); //this will throw

Also you can move std::unique_ptr to csp::owned_pointer. Please note that detecting of std::unique_ptr deletion will not work.

auto u = std::make_unique<T>();
csp::owned_pointer<T> p{std::move(u)};

assert(u.get() == nullptr);
assert(p.get() != nullptr);
u = p.unique_ptr(); // this will not throw

Smart pointer csp::owned_pointer can be copied after acquirng std::unique_ptr.

auto p = csp::make_owned<D>();
auto u = p.unique_ptr();
auto r = p;

try
{
  auto v = r.unique_ptr(); //this throws
}catch(...){}

assert(p == r);
u.reset();
assert(p == r); //this will not throw - compare operators are noexcept

try
{
  auto x = p.get(); //this throws
}catch(...){}

try
{
  auto y = r.get(); //this throws
}catch(...){}

This code was tested with g++ and clang++ compilers.

Example with google mock

struct predicate
{
  virtual bool is_true() const = 0;
  virtual ~predicate() = default;
};

struct predicate_mock : public predicate
{
  MOCK_CONST_METHOD0(is_true, bool());
};

struct cut
{
  cut(std::unique_ptr<predicate> m) : mock(std::move(m)) {}
  bool do_something(){ return mock->is_true(); }
private:
  std::unique_ptr<predicate> mock;
};

TEST(test_cut, test)
{
  using namespace testing;

  csp::owned_pointer<predicate_mock> p = csp::make_owned<StrictMock<predicate_mock>>();
  cut s{p.unique_ptr()};

  EXPECT_CALL(*p, is_true()).WillOnce(Return(true));
  ASSERT_TRUE(cut.do_something());
}

Example of usage owned_pointer with google mock, mocking factory

Because of csp::owned_pointer is copyable, it can be used with std::unique_ptr when mocking Factories methods, which return std::unique_ptr and also member functions which take std::unique_ptr as paramter. In order to do that, in gmock_macro_for_unique_ptr.hpp header there are special macros which create dummy member functions inside mock class. They are used like this:

struct item { virtual ~item() = default; };

struct factory
{
  virtual std::unique_ptr<item> create() const = 0;
  virtual ~factory() = default;
};

struct factory_mock : public factory
{
  MOCK_UNIQUE_CONST_METHOD0(create, std::unique_ptr<item>());
};

TEST(test_cut, test)
{
  using namespace testing;

  factory_mock f;
  auto p = csp::make_owned<item>();
  EXPECT_CALL(f, _create()).WillOnce(Return(p));

  auto u = static_cast<factory&>(f).create();
  ASSERT_EQ(u.get(), p.get());
}

All macros from gmock have thier equivalents in gmock_macro_for_unique_ptr.hpp to enable mocking member functions with std::unique_ptr. Those macros also support override of mocked functions, so mocking of member functions should be less error prone.

struct app { virtual ~app() = default; };

struct system
{
  virtual void install(std::unique_ptr<app>) const = 0;
  virtual ~factory() = default;
};

struct system_mock : public system
{
  MOCK_UNIQUE_CONST_METHOD1(install, void(std::unique_ptr<app>));
};

TEST(test_cut, test)
{
  using namespace testing;

  system_mock f;
  auto p = csp::make_owned<app>();

  EXPECT_CALL(f, _install(Eq(p)));
  auto u = static_cast<system&>(f).install(p.unique_ptr());

  ASSERT_NO_THROW(*p);
}

When csp::owned_pointer is created and unique_ptr() is not invoked, it can indicate a problem in test. This is why it would be good to invoke assert to indicate to the developer, that owned_pointer is owner of memory and its name don't indicate real ownership(owned_pointer). This assert is disabled by default, but it can be enabled by compiling with define OWNED_POINTER_ASSERT_DTOR.

#ifdef OWNED_POINTER_ASSERT_DTOR
assert(acquired() and
       "owned_pointer: you created owned_pointer, but unique_ptr was never acquired");
#endif