Rule A11-0-1 (advisory, implementation, automated)
A non-POD type should be defined as class.
Rationale
Types that are not POD types are supposed to be defined as class objects, as a class specifier forces the type to provide private access control for all its members by default. This is consistent with developer expectations, because it is expected that a class has its invariant, interface and could provide custom-defined constructors.
Example
// $Id: A11-0-1.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <cstdint>
#include <limits>
class A // Compliant - A provides user-defined constructors, invariant and
// interface
{
std::int32_t x; // Data member is private by default
public:
static constexpr std::int32_t maxValue =
std::numeric_limits<std::int32_t>::max();
A() : x(maxValue) {}
explicit A(std::int32_t number) : x(number) {}
A(A const&) = default;
A(A&&) = default;
A& operator=(A const&) = default;
A& operator=(A&&) = default;
std::int32_t GetX() const noexcept { return x; }
void SetX(std::int32_t number) noexcept { x = number; }
};
struct B // Non-compliant - non-POD type defined as struct
{
public:
static constexpr std::int32_t maxValue =
std::numeric_limits<std::int32_t>::max();
B() : x(maxValue) {}
explicit B(std::int32_t number) : x(number) {}
B(B const&) = default;
B(B&&) = default;
B& operator=(B const&) = default;
B& operator=(B&&) = default;
std::int32_t GetX() const noexcept { return x; }
void SetX(std::int32_t number) noexcept { x = number; }
private:
std::int32_t x; // Need to provide private access specifier for x member
};
struct C // Compliant - POD type defined as struct
{
std::int32_t x;
std::int32_t y;
};
class D // Compliant - POD type defined as class, but not compliant with
// M11-0-1
{
public:
std::int32_t x;
std::int32_t y;
};
See also
C++ Core Guidelines [11]: C.2: Use class if the class has an invariant; use struct if the data members can vary independently. stackoverflow.com [17]: When should you use a class vs a struct in C++?