PassingByValue.dox (1166B)
1 namespace Eigen { 2 3 /** \eigenManualPage TopicPassingByValue Passing Eigen objects by value to functions 4 5 Passing 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 7 With %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 9 For example, a function like this, where \c v is passed by value: 10 11 \code 12 void my_function(Eigen::Vector2d v); 13 \endcode 14 15 needs to be rewritten as follows, passing \c v by const reference: 16 17 \code 18 void my_function(const Eigen::Vector2d& v); 19 \endcode 20 21 Likewise if you have a class having an %Eigen object as member: 22 23 \code 24 struct Foo 25 { 26 Eigen::Vector2d v; 27 }; 28 void my_function(Foo v); 29 \endcode 30 31 This function also needs to be rewritten like this: 32 \code 33 void my_function(const Foo& v); 34 \endcode 35 36 Note that on the other hand, there is no problem with functions that return objects by value. 37 38 */ 39 40 }