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- namespace Eigen {
- /** \eigenManualPage TopicPassingByValue Passing Eigen objects by value to functions
- 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.
- 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.
- For example, a function like this, where \c v is passed by value:
- \code
- void my_function(Eigen::Vector2d v);
- \endcode
- needs to be rewritten as follows, passing \c v by const reference:
- \code
- void my_function(const Eigen::Vector2d& v);
- \endcode
- Likewise if you have a class having an %Eigen object as member:
- \code
- struct Foo
- {
- Eigen::Vector2d v;
- };
- void my_function(Foo v);
- \endcode
- This function also needs to be rewritten like this:
- \code
- void my_function(const Foo& v);
- \endcode
- Note that on the other hand, there is no problem with functions that return objects by value.
- */
- }
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