chore: add files from master-wiki repo

_master_wiki/void/notes/iterators.md

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+# iterators
+
+> The iterator pattern allows you to perform some task on a sequence of items
+> in turn. An iterator is responsible for the logic of iterating over each item
+> and determining when the sequence has finished.
+[Rust book](https://doc.rust-lang.org/book/ch13-02-iterators.html)
+
+An itetarator it's usually related to some sort of lists, vectors or collection
+of items, but the iterator can be anything that implements the interface. The
+interaface depends on the language, but usually only needs a `next(Self) -> Item`
+method that returns the next item to be acted upon.
+
+The adventage of iterators is that you can use them with anything that accept
+thems (kinda in the reusable side of programming), and modern standard
+libraries implements patterns to use them like: `forEach`, `map`, `sum`, etc
+
+Another common use case is to iterate on something indefinetly as long as it
+continue to provide new items. For example you can implement a
+`PollingIterator` that fetch data from a remote source until the source says
+there's no more data:
+
+```python
+class EmailPoll:
+    """Iterator class that pools emails from the EmailService indefinetly."""
+
+    def __init__(self, service: EmailService, wait_time: int):
+        super(EmailPoll, self).__init__()
+        self.service = service
+        self.wait_time = wait_time
+        self.current_mails = self.service.fetch_emails()
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        while len(self.current_mails) == 0:
+            self.current_mails = self.service.fetch_emails()
+
+            if len(self.current_mails) == 0:
+                print(f"No new emails, waiting {self.wait_time}s")
+                sleep(self.wait_time)
+
+        return self.current_mails.pop(0)
+
+
+email_service = EmailService()
+for mail in EmailPoll(email_service, 3):
+    print(mail)
+
+```