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Say we have an abstract class Foo declared as so: class Foo { public: virtual void test() = 0; }; Let's say that we make a derived concrete class FooDerived, and decide to mark it's ve...
#1: Initial revision
by
Moshi
·
2022-05-05T08:25:17Z (over 2 years ago)
Why can't a derived class add a const qualifier to a method?
Say we have an abstract class `Foo` declared as so:
```cpp
class Foo {
public:
virtual void test() = 0;
};
```
Let's say that we make a derived concrete class `FooDerived`, and decide to mark it's version of `test` as `const` as it doesn't modify its state.
```cpp
class FooDerived : public Foo {
public:
void test() const override { std::cout << "FooDerived!" << std::endl; }
};
```
```
main.cpp:12:10: error: ‘void FooDerived::test() const’ marked ‘override’, but does not override
```
Why is this not allowed? I thought that it would be, given that the only real function of the qualification is to be able to be called on const instances. It shouldn't be any more restrictive on the caller than the non-const version. Also, is there a good way to achieve this?