Add recursiveMap(_:)

[SusanDoggie]

add recursiveMap() method.

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[CTMacUser]

Is a "recursive mapped sequence" a term of art for a particular structure? I've never heard of it before, and the documentation so far assumes you pretty much already know. A quick web search found something related using the Python language; is the code here supposed to be a Swift adaptation of the Python code?

The concept seems to be a way to do tree traversal without that type having to provide its own depth- and breath-first iterators; you just have to supply a function to map an element to a Sequence of its children, and this function takes care of the rest.

[SusanDoggie]

Is a "recursive mapped sequence" a term of art for a particular structure? I've never heard of it before, and the documentation so far assumes you pretty much already know. A quick web search found something related using the Python language; is the code here supposed to be a Swift adaptation of the Python code?

The concept seems to be a way to do tree traversal without that type having to provide its own depth- and breath-first iterators; you just have to supply a function to map an element to a Sequence of its children, and this function takes care of the rest.

This method is simplified recursive CTE, which can map a hierarchical table to a linear sequence.

I don’t known what’s the name of this operation. So I call it recursive map.

[ssouzawallace]

Without further proof of time and space complexity. This PR IMO is unmeargeable.
Even though it could be a good addition. I firstly thought that this would apply to any Sequence. However. Looks like this is a special case of Colletion and maybe not Sequence.
Having to conform to RecursiveMapSequence seems like too much trouble for a rare case in this protocol.
But as I said. Maybe it fits better with Collection or similar.

-/+ 1 - The Node struct example is not properly written for official docs.

[ssouzawallace]

@SusanDoggie
I'm kinda skeptic this func is actually O(1) for time-complexity. Or any recursive function. Unles I'm missing a rare 0.00001% case. Are you sure about that L47 statement?

Could you demonstrate if possible?

Looks like it is at least O(n). But what is n? Is n self.count? Is n the whole tree size i.e. all nodes from self.

Also VERY IMPORTANT*! It doesn't look like your Node struct example is conforming with Sequence or RecursiveMapSequence at all.

Other than that. Interesting use case you put there and awesome work with putting this so much ready for official documentation.

[ssouzawallace]

@SusanDoggie Also. Tip. If you plan on keeping this PR up-to-date. I suggest squash commits, make them atomic commits, all properly signed.