1namespace Eigen { 2 3/** \eigenManualPage TopicPassingByValue Passing Eigen objects by value to functions 4 5Passing objects by value is almost always a very bad idea in C++, as this means useless copies, and one should pass them by reference instead. 6 7With %Eigen, this is even more important: passing \ref TopicFixedSizeVectorizable "fixed-size vectorizable Eigen objects" by value is not only inefficient, it can be illegal or make your program crash! And the reason is that these %Eigen objects have alignment modifiers that aren't respected when they are passed by value. 8 9For example, a function like this, where \c v is passed by value: 10 11\code 12void my_function(Eigen::Vector2d v); 13\endcode 14 15needs to be rewritten as follows, passing \c v by const reference: 16 17\code 18void my_function(const Eigen::Vector2d& v); 19\endcode 20 21Likewise if you have a class having an %Eigen object as member: 22 23\code 24struct Foo 25{ 26 Eigen::Vector2d v; 27}; 28void my_function(Foo v); 29\endcode 30 31This function also needs to be rewritten like this: 32\code 33void my_function(const Foo& v); 34\endcode 35 36Note that on the other hand, there is no problem with functions that return objects by value. 37 38*/ 39 40} 41