CODEWITHSUNDEEP
c++compiler-errorsoperator-overloading
user173342
user173342

Reputation: 1840

Inherited operator= not working?

I am overloading operator= on a struct EqualTestBase, and operator= takes different parameters than are used to construct the struct.

struct EqualTestBase
{
 EqualTestBase(int one) {}

 EqualTestBase& operator=(std::string two)
 {
  //stuff

  return *this;
 }
};

It works fine on the base class. But a trival struct derived from it, EqualTestDerived, acts like it doesn't have the operator= member function.

struct EqualTestDerived : public EqualTestBase
{
 EqualTestDerived(int one) : EqualTestBase(one) {}
};

void test()
{
 EqualTestBase basetest(0);
 basetest = "test"; //this is fine, compiles

 EqualTestDerived derivedtest(0);
 derivedtest = "test"; //this does not compile, says there is no constructor that takes type const char[5]
}

Do I have to redefine operator= on all derived structs, or is there a way to automatically pass down that functionality?

Upvotes: 0

Views: 51

Answers (2)

Jerry Coffin
Jerry Coffin

Reputation: 490338

operator= isn't inherited. If a class doesn't define operator= itself, the compiler will synthesize one for it (regardless of the fact that its base class does define an operator=).

If you want something that can be inherited (and can be virtual) you generally want to define it as a function with a different name. The generally accepted name for such a function is clone (though clone is normally more like a copy constructor, creating a new instance of an object, not just assigning to an existing one).

Upvotes: 2

Mike Seymour
Mike Seymour

Reputation: 254621

The derived class has an implicitly-declared copy-assignment operator, which hides the one declared in the base class. You can use using to bring it into scope:

struct EqualTestDerived : public EqualTestBase
{
    EqualTestDerived(int one) : EqualTestBase(one) {}
    using EqualTestBase::operator=;
};

Upvotes: 5

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