Add Create A Module Of Utility Functions as a Ruby TIL

ruby/create-a-module-of-utility-functions.md

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+# Create A Module Of Utility Functions
+
+In my [latest blog post](https://www.visualmode.dev/create-a-module-of-utility-functions-in-ruby),
+I went into full detail about how the [`Module#module_function` method](https://ruby-doc.org/3.4.1/Module.html#method-i-module_function) works.
+It creates both a module of utility functions that we can access directly on
+that module like we would with `self` methods. It can also be included in a
+class as a way of sharing copies of those utility functions with the class. A
+key point to them being copies is that they can then be overridden by the
+including class.
+
+Here is the example I used in the blog post:
+
+```ruby
+module MarkdownHelpers
+  module_function
+
+  def heading(text, level = 1)
+    ("#" * level) + " #{text}"
+  end
+
+  def link(text, href)
+    "[#{text}](#{href})"
+  end
+
+  def image(alt_text, href)
+    "!#{link(alt_text, href)}"
+  end
+end
+```
+
+I won't cover everything that the blog post covers, but what I found really nice
+about this pattern is that I can call those utility functions directly with the
+module as the receiver:
+
+```bash
+$ ruby -r ./markdown_helpers.rb -e 'puts MarkdownHelpers.link("Click here", "https://example.com")'
+[Click here](https://example.com)
+```
+
+The alternative to this generally looks like:
+
+```ruby
+module MarkdownHelpers
+  def self.heading(text, level = 1)
+    ("#" * level) + " #{text}"
+  end
+
+  def self.link(text, href)
+    "[#{text}](#{href})"
+  end
+
+  def self.image(alt_text, href)
+    "!#{link(alt_text, href)}"
+  end
+end
+```
+
+That would be fine, but we completely lose out on the ability to include it as a
+mix-in with other classes.