Trying to understand Exercism’s Acronym solution

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Elixir Exercism Acronym

I am working to understand xianrusso’s solution to Exercism’s Acronym solution.

defmodule Acronym do
  def abbreviate(string) do
    Regex.scan(~r/(?<![A-Z])[A-Z]|(?<!\')\b[a-z]/, string)
    |> List.flatten
    |> Enum.map(&String.upcase/1)
    |> Enum.join
  end
end

The portion that I am working to digest is the Regex.

I believe this link contains the answer I just want to confirm that what I am thinking is happening is indeed what is happening. Advanced Regex Tutorial—Regex Syntax

I believe that in this ~r/(?<![A-Z])[A-Z]/ - that the (?<![A-Z]) is saying that as long as where we are at in the string does not have a capital letter that immediately precedes it then we can continue to keep matching it to [A-Z].

I believe that in this ~r/(?<!’)\b[a-z]/ it is saying that as long as where we are at in the string there is not a ’ that precedes it then we can keep matching it to \b[a-z]

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quiet, but note that \b is s zero-width (same as lookbehinds) assertion, which is a word boundary. A limit between \w (a word) and a non-word (\W), or the beginning or end of a word.
So the second part of the regex is telling you [a-z] preceeded by any non-word that is not a single quote, and it can match a [a-z] at the beginning of the string.

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The regex commented out in plain English:

regex =  ~r/
  (?<![A-Z])[A-Z]  # Match ONE uppercase letter from A to Z,
                   # that is not preceded by another uppercase letter from A to Z.

  |                # OR

  (?<!\')        # no need to escape the single quote  
  \b
  [a-z]          # Match ONE lowercase letter from a to z,
                   # that is preceded by a word boundary (\b)
                   # and that is not preceded by a single quote.
                   # Note: the beginning of a string is considered a word boundary.
  /x               # "x" modifier to to allow comments

Note the regex is valid, feel free to use it in your code, if you want.

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Thank you!

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No worries

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