A9-3-1 - Unofficial Autosar C++ Guidelines Reference

Rule A9-3-1 (required, implementation, partially automated)

Member functions shall not return non-const “raw” pointers or references to private or protected data owned by the class.

Rationale

By implementing class interfaces with member functions the implementation retains more control over how the object state can be modified and helps to allow a class to be maintained without affecting clients. Returning a handle to data that is owned by the class allows for clients to modify the state of the object without using an interface. Note that this rule applies to data that are owned by the class (i.e. are class-data). Nonconst handles to objects that are shared between different classes may be returned.

See: Ownership.

Exception

Classes that mimic smart pointers and containers do not violate this rule.

Example

// $Id: A9-3-1.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <cstdint>
#include <memory>
#include <utility>
class A
{
public:
explicit A(std::int32_t number) : x(number) {}
// Implementation
std::int32_t&
GetX() noexcept // Non-compliant - x is a resource owned by the A class
{
return x;
}

private:
std::int32_t x;
};
void Fn1() noexcept
{
A a{10};
std::int32_t& number = a.GetX();
number = 15; // External modification of private class data
}
class B
{
public:
explicit B(std::shared_ptr<std::int32_t> ptr) : sharedptr(std::move(ptr)) {}
// Implementation
std::shared_ptr<std::int32_t> GetSharedPtr() const

noexcept // Compliant - sharedptr is a variable being shared between
// instances

{

return sharedptr;

}

private:
std::shared_ptr<std::int32_t> sharedptr;

};
void Fn2() noexcept
{
std::shared_ptr<std::int32_t> ptr = std::make_shared<std::int32_t>(10);
B b1{ptr};
B b2{ptr};

*ptr = 50; // External modification of ptr which shared between b1 and b2

// instances
auto shared = b1.GetSharedPtr();

*shared = 100; // External modification of ptr which shared between b1 and

// b2 instances
}
class C
{
public:
explicit C(std::int32_t number)
: ownedptr{std::make_unique<std::int32_t>(number)}
{
}
// Implementation
const std::unique_ptr<std::int32_t>& GetOwnedPtr() const
noexcept // Non-compliant - only unique_ptr is const, the object that
// it is pointing to is modifiable
{
return ownedptr;
}
const std::int32_t& GetData() const noexcept // Compliant
{

return *ownedptr;

}

private:
std::unique_ptr<std::int32_t> ownedptr;

};
void Fn3() noexcept
{
C c{10};
const std::int32_t& data = c.GetData();
// data = 20; // Can not modify data, it is a const reference
const std::unique_ptr<std::int32_t>& ptr = c.GetOwnedPtr();

*ptr = 20; // Internal data of class C modified

}

Unofficial Autosar C++ Guidelines Reference

Rationale

Exception

Example

See also