Consistent interface of container class for element access

[jslee02]

DART has many container classes. For example, Skeleton is a container of BodyNode and Marker, and Joint is a container of DegreeOfFreedom. To access the elements of the containers, there are two styles of interface: (1) getNum(Object)() / getObject(index) and (2) const vector getObjects(). Some container provide only (1), others provide (2), and some provide both, which is not consistent.

I would like to propose to have a consistent interface or, at least, have an interface that returns an iterable object like std::vector<Object*>. With the iterable object, we can utilize the advantage of ranged-based for loop of C++11, which provides a neater way of iterating the elements.

Also, in most cases, container classes return const reference of the iterable object that contains const/non-const pointers like const std::vector<BodyNode*>& and const std::vector<const BodyNode*>&. For this, two ways are used: (1) having two iterable objects in it, (2) return a const_cast-ed copy of the iterable object. Both of them have downsides: (1) requires unnecessary memory, and (2) requires unnecessary computation for creating the iterable object every time the accessor is called.

To resolve this, I'd like to propose a wrapper class of pointer container that provides a customized iterator for const_cast when the element is accessed instead of holding the copy of const_cast-ed elements inside it. I thought there must be others having a similar issue and reasonable solution, but couldn't find. Please let me know if it's not.

Here is a brief sketch of the wrapper class with tests.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[jslee02]

Resolved by #1644