Add Get The Names Of The Month as a Ruby TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1665 TILs and counting..._
+_1666 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -1358,6 +1358,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Generate Ruby Version And Gemset Files With RVM](ruby/generate-ruby-version-and-gemset-files-with-rvm.md)
 - [Get Info About Your RubyGems Environment](ruby/get-info-about-your-ruby-gems-environment.md)
 - [Get Specific Values From Arrays And Hashes](ruby/get-specific-values-from-hashes-and-arrays.md)
+- [Get The Names Of The Month](ruby/get-the-names-of-the-month.md)
 - [Get The Output Of Running A System Program](ruby/get-the-output-of-running-a-system-program.md)
 - [Get UTC Offset For Different Time Zones](ruby/get-utc-offset-for-different-time-zones.md)
 - [Identify Outdated Gems](ruby/identify-outdated-gems.md)

ruby/get-the-names-of-the-month.md

@@ -0,0 +1,24 @@
+# Get The Names Of The Month
+
+Ruby's `Date` object has a `MONTHNAMES` constant that returns an array of names
+of the month. You'd think that means the array contains 12 items. However, the
+size of that array is 13.
+
+```ruby
+> Date::MONTHNAMES
+=> [nil, "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
+```
+
+Notice it has all 12 months, plus an initial value of `nil`.
+
+This is because it allows us to more intuitive access a month by it's index
+without having to do a little subtraction. If I want to know what the 9th month
+is, I can do an array access for `9`.
+
+```ruby
+> Date::MONTHNAMES[9]
+=> "September"
+```
+
+Because arrays in Ruby use 0-based indexing, without this baked in `nil` value,
+you'd instead get `"October"` when passing in `9`.