Is there a way to prevent a method from being overridden in subclasses?

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When you can use the final specifier for virtual methods (introduced with C++11), you can do it. Let me quote my favorite doc site:

When used in a virtual function declaration, final specifies that the function may not be overridden by derived classes.

Adapted to your example that’d be like:

class Base {
public:
    virtual bool someGuaranteedResult() final { return true; }
};

class Child : public Base {
public:
    bool someGuaranteedResult() { return false; /* Haha I broke things! */ }
};

When compiled:

$ g++ test.cc -std=c++11
test.cc:8:10: error: virtual function ‘virtual bool Child::someGuaranteedResult()’
test.cc:3:18: error: overriding final function ‘virtual bool Base::someGuaranteedResult()’

When you are working with a Microsoft compiler, also have a look at the sealed keyword.

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