I know it has probably been asked a million times here, but I couldn't find any example that I could use. I want to create an unordered_map whose key is an object that I made (vector2), what's the best way of implementing a hash function to it? Can I have an example? struct vector2 { vector2(); vector2(const vector2 &v2); vector2(float fx, float fy); vector2 operator * (float num) const; vector2 operator * (const vector2& v2) const; vector2 operator / (float num) const; vector2 operator / (const vector2& v2) const; vector2 operator - (float num) const; vector2 operator - (const vector2& v2) const; vector2 operator + (float num) const; vector2 operator + (const vector2& v2) const; bool operator == (const vector2& v2) const; bool operator != (const vector2& v2) const; vector2& operator += (const vector2& v2); vector2& operator -= (const vector2& v2); vector2& operator *= (float f); vector2& operator /= (float f); float x,y; }; boost::unordered_map<vector2, int> won't work.