A13-5-1 - Unofficial Autosar C++ Guidelines Reference

Rule A13-5-1 (required, implementation, automated)

If “operator[]” is to be overloaded with a non-const version, const version shall also be implemented.

Rationale

A non-const overload of the subscript operator allows an object to be modified, by returning a reference to member data, but it does not allow reading from const objects. The const version of “operator[]” needs to be implemented to ensure that the operator can be invoked on a const object. Note that one can provide a const version of operator[] (to support read-only access to elements), but without a non-const version.

Example


// $Id: A13-5-1.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <cstdint>

class Container1
{
public:
std::int32_t& operator[](
std::int32_t index) // Compliant - non-const version
{
return container[index];
}
std::int32_t operator[](
std::int32_t index) const // Compliant - const version
{
return container[index];
}

private:
static constexpr std::int32_t maxSize = 10;
std::int32_t container[maxSize];
};
void Fn() noexcept
{
Container1 c1;
std::int32_t e = c1[0]; // Non-const version called
c1[0] = 20;
// Non-const version called
Container1 const c2{};
e = c2[0]; // Const version called
// c2[0] = 20; // Compilation error
}
class Container2 // Non-compliant - only non-const version of operator[]
// implemented
{
public:
std::int32_t& operator[](std::int32_t index) { return container[index]; }

private:
static constexpr std::int32_t maxSize = 10;
std::int32_t container[maxSize];
};

Unofficial Autosar C++ Guidelines Reference

Rationale

Example

See also