Add Decompose Unicode Character With Diacritic Mark as a Ruby TIL

ruby/decompose-unicode-character-with-diacritic-mark.md

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+# Decompose Unicode Character With Diacritic Mark
+
+A character like the `ñ` is typically represented by the unicode codepoint of
+`U+00F1`. However, it is also possible to represent it with two unicode
+codepoints -- the `n` (`U+006E`) and the combining diacritical mark `˜`
+(`U+0303`).
+
+We can see that by comparing a typed `ñ` with one where we split it apart into
+the separate codepoints. We can do that with
+[`#unicode_normalize`](https://apidock.com/ruby/v2_5_5/String/unicode_normalize)
+and the `:nfd` argument which stands for _Normalized Form Decomposed_.
+
+```ruby
+> "ñ" == "ñ".unicode_normalize(:nfd)
+=> false
+> "ñ".unicode_normalize(:nfd).length
+=> 2
+> "ñ".length
+=> 1
+```
+
+We can inspect the exact codepoints by iterating over each character and
+printing out the codepoint value.
+
+```ruby
+"ñ".each_char.with_index do |char, i|
+  puts "#{i}: '#{char}' -> U+#{char.ord.to_s(16).upcase.rjust(4, '0')}"
+end
+# 0: 'ñ' -> U+00F1
+# => "ñ"
+
+"ñ".unicode_normalize(:nfd).each_char.with_index do |char, i|
+  puts "#{i}: '#{char}' -> U+#{char.ord.to_s(16).upcase.rjust(4, '0')}"
+end
+# 0: 'n' -> U+006E
+# 1: '̃' -> U+0303
+#=> "ñ"
+```
+
+Notice the difference after the character has been decomposed such that the
+diacritic is separated from the character.
+
+This can be done with other characters containing diacritics.
+
+And here we go the other direction with
+[`#pack`](https://ruby-doc.org/core-3.0.1/Array.html#method-i-pack).
+
+```ruby
+> [0x006E, 0x0303].pack("U*")
+=> "ñ"
+> [0x00F1].pack("U*")
+=> "ñ"
+> [0x006E, 0x0303].pack("U*") == [0x00F1].pack("U*")
+=> false
+```