Why is this an issue?
Mixing (non-const) public and private data members is a bad practice because it causes confusion about the intention of
the class:
- If the class is a collection of loosely related values, all the data members should be
public.
- On the other hand, if the class is trying to maintain an invariant, all the data members should be
private.
If we mix data members with different levels of accessibility, the purpose of the class is muddled.
Noncompliant code example
class MyClass // Noncompliant
{
public:
int firstNumber1() const { return firstNumber; }
void setFirstNumber(int firstNumber) { this->firstNumber = firstNumber; }
int secondNumber = 2;
const int constNumber = 0; // const data members are fine
private:
int firstNumber = 1;
};
Compliant solution
class MyClass // Depending on the case, the solution might be different. Here, since this class does not enforce any invariant, we make all the data members public
{
public:
int firstNumber;
int secondNumber;
const int constNumber = 0;
};
Exceptions
Since const data members cannot be modified, it’s not breaking encapsulation to make a const value public, even in a class that
enforces an invariant.
Resources
