These two are not the same - String.split with an empty string splits on graphemes, which are a further unit bigger than codepoints.

The rules for clustering codepoints into graphemes are defined by the Unicode standards, and the code for handling them is generated from canonical text files.

iex(4)> String.codepoints("🇺🇸")
["🇺", "🇸"]
iex(5)> String.split("🇺🇸", "", trim: true)
["🇺🇸"]
iex(6)> "🇺🇸" <><<0>>
<<240, 159, 135, 186, 240, 159, 135, 184, 0>>

The single displayed character is a grapheme, composed of two codepoints U+1F1FA and U+1F1F8, represented by 8 bytes.

Another way that codepoints and graphemes can diverge is combining characters; for instance, U+0308 is “Combining Diaresis” which will add ¨ to the preceding character. Example:

iex(9)> s = "ca\u0308t"
"cät"
iex(10)> String.codepoints(s)
["c", "a", "̈", "t"]
iex(11)> String.split(s, "", trim: true)
["c", "ä", "t"]

(note that the combining character prints very oddly when isolated inside ")

• bitstrings are everything what can be represented using <<>>
• binaries are bitstringths which length is a multiple of 8
• Strings are binaries which bytes represent valid utf-8 encoded codepoints.

First 2 terms are from Erlang

FWIW, there is nowhere in the docs with that line. If they were, they would indeed be incorrect.

Other than that, you are right, codepoints are integers. String.codepoints returns codepoints as UTF-8 encoded binaries, i.e. codepoints as strings. The precise definition of this would be “code unit” but we wanted to avoid introducing yet another term. I have updated the docs to make it clear that String.codepoints returns an encoded representation, not integers. Thanks.

Just to make sure we’re on the same page, charlists and binaries are entirely different data structures. Charlists are lists of integers, where each integer is a valid code point. A charlist is an actual list through, in a is_list(list) #=> true sense. Binaries are not lists, even a little bit.

A bitstring is a fundamental data type, denoted with the syntax <<>>. It is a contiguous sequence of bits in memory.

A binary is a byte aligned bitstring, which is to say it is a sequence of whole bytes. They can be any bytes at all.

A string is a binary where all the bytes form a valid UTF8 sequence.

Thank you all for your input – this has been very educational. I have submitted a PR to the https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html page that I hope will better explain the concepts at play here.