Sorry for a ton of edits. Made a quick and dirty version and then figured I will write it as if I am paid for it.
dimitarvp
dimitarvp
Better come visit the forum and copy-paste from here and not from the email because I made a lot of edits.
1
NobbZ
Now as we have more information, I have an alternative version which I prefer over @dimitarvp, because it is much more explicit about what we want.
- It says that we want an URL and verifies we get one (by parsing it) and that we are only interested in the
path, - it says that we are searching for dot, followed by at least one digit and ending with a slash as the last character of the path, but we are only interested in the actual digits (the call to
Regex.named_captures/3), - we want those digits to cleanly parse into a number.
If all succeed, we return an :ok-tuple, and simply :error otherwise.
But which version to choose is probably a matter of taste, I have not benchmarked them.
defmodule M do
def extract(url) do
with %URI{path: path} when is_binary(path) <- URI.parse(url),
%{"num" => num_str} <- Regex.named_captures(~r[\.(?<num>\d+)/$], path),
{num, ""} <- Integer.parse(num_str) do
{:ok, num}
else
_ -> :error
end
end
end
IO.inspect M.extract("https://foster.com/death-pancake.1468/")
IO.inspect M.extract("https://hkd33.net/mr-rogers101.690153/")
IO.inspect M.extract("https://space-force911.gov/sauce-master.13257777/")
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dimitarvp
The reasons I did not do it like you:
- I worked with governmental datasets before. Some have very blatant errors or peculiarities in them, like spaces in the domain part of the URLs, three forward slashes at the end, two dots instead of one etc… Some of them really don’t care. As an extreme example ~17 years ago, a guy reported how he had to make his own mini-parser for malformed RSS from several agencies (that “RSS” was not even a valid XML).
- Regexes can become a scaling problem if you have to process a lot of data. But I will admit that I am on the side of some preliminary optimization here which is a 50/50 decision and depends on a lot of factors.
That being said, I like your code. 
2
dimitarvp
@makeitrein this is not StackOverflow and we are not collecting reputation points but – whichever solution you like, please mark it up as the answer. It increases the visibility of such topics on the forum and people in the future can make use of your question and our answers.
1
NobbZ
Legacy… No need to justify whether it’s governmental or not, legacy is a pain on its own so often, but usually I just assume everything is conforming the corresponding specifications until I get proven wrong.
2
dimitarvp
Yep. I guess I am older and grumpier and just flat out assume people don’t know what they are doing. 
But you are correct, we should be enforcing standards until we really have no other choice. Agreed.
2
makeitrein
@NobbZ and @dimitarvp - just woke up to the pleasant surprise of two discrete solutions that, in the words of the late Steve Jobs, would be insanely great! Always a fan of getting input & insight from the more seasoned programmers on some of my junior code, gets me exposed to a few new patterns and methods along the way.
@dimitarvp takes the award for the problem, but just by a bit. I find his code slightly more grokable, especially if I were to revisit it a few months down the line. It doesn’t seem that I can mark responses as answers… here is what I see on my end…
0
NobbZ
I moved it to Questions & Help, also I put codereview tag onto it and regular expression. OP should be able to accept an answer now.
0
OvermindDL1
That’s an understatement, like how about CSV files where there is no quotations, so if a comma is in a string in a cell then it all gets thrown off, and I still have to support it and read it properly! Yes it’s a horror, yes so so many secondary checks… >.>
1