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-array is a module which enables fixed sized arrays to be created in the Wren programming language. Although the size of the array is fixed, the elements themselves can be mutated. It consists of three classes: Array, ArrayType and BitArray. The second of these enables one to create a named type which inherits from Array dynamically at runtime and the third class enables one to create a compressed array of boolean values.
It is the twenty-eighth 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.
To use it you need to copy the source code (in the talk page) to a text file called array.wren and place this in the same directory as the importing script so the command line interpreter can find it.
As there is a dependency on the Wren-check module, you also need to copy that (if it is not already present) to the same directory as described here. There is also a dependency on the Meta module which is an optional part of Wren's standard library but is included in Wren-cli by default.