Rule A10-3-5 (required, implementation, automated)
A user-defined assignment operator shall not be virtual.
Rationale
If an overloaded operator is declared virtual in a base class A, then in its subclasses B and C identical arguments list needs to be provided for the overriders. This allows to call an assignment operator of class B that takes an argument of type C which may lead to undefined behavior. Note that this rule applies to all assignment operators, as well to copy and move assignment operators.
Example
// $Id: A10-3-4.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
class A
{
public:
virtual A& operator=(A const& oth) = 0;
// Non-compliant
virtual A& operator+=(A const& rhs) = 0; // Non-compliant
};
class B : public A
{
public:
B& operator=(A const& oth) override // It needs to take an argument of type
// A& in order to override
{
return *this;
}
B& operator+=(A const& oth) override // It needs to take an argument of
// type A& in order to override
{
return *this;
}
B& operator-=(B const& oth) // Compliant
{
return *this;
}
};
class C : public A
{
public:
C& operator=(A const& oth) override // It needs to take an argument of type
// A& in order to override
{
return *this;
}
C& operator+=(A const& oth) override // It needs to take an argument of
// type A& in order to override
{
return *this;
}
C& operator-=(C const& oth) // Compliant
{
return *this;
}
};
// class D : public A
//{
// public:
//D& operator=(D const& oth) override // Compile time error - this method
//does not override because of different
//
signature
//
{
return *this;
//
//
}
//D& operator+=(D const& oth) override // Compile time error - this method
//does not override because of different
//
signature
//
{
return *this;
//
//
}
//};
void Fn() noexcept
{
B b;
C c;
b = c;
// Calls B::operator= and accepts an argument of type C
b += c; // Calls B::operator+= and accepts an argument of type C
c = b;
// Calls C::operator= and accepts an argument of type B
c += b; // Calls C::operator+= and accepts an argument of type B
// b -= c; // Compilation error, because of types mismatch. Expected
// behavior
// c -= b; // Compilation error, because of types mismatch. Expected
// behavior
B b2;
C c2;
b -= b2;
c -= c2;
}
See also
none