[V3] Extract Concepts from v2 exercise Flatten Array

[goalaleo]

Extract the list of concepts required to solve the v2 ruby exercise: flatten-array. For each concept, describe why it is required to solve the exercise. Keep in mind that an exercise can have multiple approaches. The goal of this task is to help determine the total list of concepts that make up flatten-array.

The list of concepts should be stored in the following document: languages/ruby/reference/exercise-concepts/flatten-array.md Use this link to create a PR to add this document.

[kotp]

Should the body of this issue follow the template [as shown here]? What I did for exercism/ruby#1070 was copied the template body, edited the main comment and set that in there.

It provides the location for the V3 Readme as well...

[goalaleo]

Thanks @kotp I created the PR when the template didn't exist yet, so I left the description empty. It's now updated

[kytrinyx]

I've done a bit of a deep dive on the various processes that different tracks have followed when developing their syllabus, and one of the things that I learned is that trying to come up with a full list of concepts up front was less successful than we had hoped it would be.

In general the most successful approach seemed to use a "just in time" strategy, working from the root of the concept tree, identifying a small handful of concepts that were not too far ahead in the tree, and then filling gaps where necessary.

I'm going to go ahead and close this issue. If someone wants to work on concept exercises, please open an issue and we can help identify a good concept to tackle, as well as provide some guidance on how to proceed from there.