From Rosetta Code
This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.

Wren-trait is a module which provides the abstract classes: Comparable, Cloneable and CloneableSeq. The first of these enables child classes to easily support the basic comparison operators and the latter two enables such classes to identify themselves as cloneable given a suitable mechanism.

It also contains the wrapper classes: Stepped, Reversed, Indexed, ByRef and ByKey plus a helper class SeqEntry. The first two of these enable sequences to be iterated in either (or both) a stepped fashion (steps > 1) or in reverse. The third enables the iteration to include the zero-based index of the sequence elements and SeqEntry assists with this.

ByRef enables a value to be passed by reference to a method or function and ByKey enables a reference type object to be used as a Map key.

It is the fifth in a series of modules (listed on the language's main page) designed to assist with writing Rosetta Code tasks so the same code does not have to be written or copy/pasted time and time again thereby bloating a task's script code unnecessarily. It is also small enough to be used by other modules in the series which are usually organized and written to avoid inter-dependencies.

To use it all you need to do is to copy the source code (in the talk page) to a text file called trait.wren and place this in the same directory as the importing script or module so the command line interpreter can find it.