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POc++: Inheriting a method with a different (but covariant) return type
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copied! <p>Suppose we have 2 classes:</p> <pre class="lang-cpp prettyprint-override"><code>class DataStructure { public: DataStructure &operator=(const DataStructure &); friend const DataStructure &operator+(int, const DataStructure &); //... }; class Array : public DataStructure { public: Array &operator=(const DataStructure &); friend const Array &operator+(int, const Array &); //... }; </code></pre> <p>and we want <code>Array::operator=</code> and <code>Array</code>'s freind <code>operator+</code> to do the same thing as <code>DataStructure::operator=</code> and <code>DataStructure</code>'s freind <code>operator+</code>, except they should return <code>Array &</code>,<code>const Array &</code> instead of <code>DataStructure &</code>,<code>const DataStructure &</code>. I need to do it with dozens of methods, so is there a simpler way to implement it than the following?</p> <pre class="lang-cpp prettyprint-override"><code>Array &Array::operator=(const DataStructure &other) { return (Array &)DataStructure::operator=(other); } const Array &operator+(int x, const Array &other) { return (const Array &)(x + (DataStructure)other); } </code></pre> <hr/> <p><strong>EDIT:</strong> I came up with another idea, although it's a pretty bad one:</p> <pre class="lang-cpp prettyprint-override"><code>class Array; class DataStructure { public: //... operator Array &() const; }; //... DataStructure::operator Array &() const { return (Array &)*this; } </code></pre> <p>This way <code>DataStructure</code> is implicitly converted to an <code>Array</code> whenever needed, although it still can't handle correctly cases where both <code>DataStructure</code> and <code>Array</code> are legal but do different things, as in this example:</p> <pre class="lang-cpp prettyprint-override"><code>//in class DataStructure: public: friend ostream &operator<<(ostream &os,const DataStructure &) { os << "DataStructure" << endl; return os;} //in class Array: public: friend ostream &operator<<(ostream &os,const Array &) { os << "Array" << endl; return os;} //... int main() { Array x; cout << 1 + x << endl; // output: "DataStructure" instead of "Array" return 0; } </code></pre> <p>Thanks you!</p>

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