C++ force override

Question

I have some class, like

class object {
public:
virtual std::string name() const; 
};

It provides some interface, and I want all derivated to override method name. Problem is, it is not overriden, nothing breaks at compile time, but I get problems in run-time. Is it any way to enforce method overriding? EDIT: I want to enforce overriding in all derivates, not just direct descedants!

I question that this would build correctly. You should be getting linker errors. — Kerrek SB, Aug 15 '12 at 10:08
Yes, I did not printed definition. Why? It's all about interfaces. — KAction, Aug 15 '12 at 10:10
RTTI type_info::name is compiler-specific. I need to have fixed string. — KAction, Aug 15 '12 at 10:18
@KerrekSB: already std::string and not being defined inlnie as constexpr should error out — PlasmaHH, Aug 15 '12 at 10:34
@illusionoflife: There is no way to enforce this for all derived classes which does not require you to add code for each derived class, except documentation and human brain. — smerlin, Aug 15 '12 at 10:50
see this answer http://stackoverflow.com/a/9661580/819272 for an attempt to force all derived classes to override — TemplateRex, Aug 15 '12 at 10:52
I dont understand how that solution would work, the ctor there would accept any function with the same signature, it wont have to override `foo()` specificaly — Gir, Aug 15 '12 at 11:42

score 8 · Answer 1 · answered Aug 15 '12 at 10:03

8

Yes, make it a pure virtual:

constexpr virtual std::string name() = 0;

answered Aug 15 '12 at 10:03

ecatmur

152,476
27
293
366

1

And so what? It enforce overriding in first derivate, not all subsequent! – KAction Aug 15 '12 at 10:09
@illusionoflife you didn't specify that requirement in your question. – ecatmur Aug 15 '12 at 10:12
`all derivated`. Well, probably it is not obvilous. Will edit. – KAction Aug 15 '12 at 10:15

score 6 · Accepted Answer · answered Aug 15 '12 at 10:41

6

You can check whether a member is defined in a base class by checking its pointer-to-member type:

static_assert(std::is_same<decltype(&U::name), std::string (U::*)()>::value,
              "name must be defined directly in U");

This does mean that at compile time you must have access to all the descendant types that you're interested in.

answered Aug 15 '12 at 10:41

ecatmur

152,476
27
293
366

Well, it requires to add code into descendants, not into object. But it will still help. Thank! – KAction Aug 15 '12 at 10:45

C++ force override

2 Answers2