From 1c4707c18f97c60b96e43e1233a21d81ef232c11 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Thu, 28 Feb 2019 19:31:45 -0600
Subject: [PATCH] Add Comparing DateTime Structs as an elixir til

---
 README.md                            |  3 ++-
 elixir/comparing-datetime-structs.md | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 elixir/comparing-datetime-structs.md

diff --git a/README.md b/README.md
index a4cc82a..df58eac 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_774 TILs and counting..._
+_775 TILs and counting..._
 
 ---
 
@@ -123,6 +123,7 @@ _774 TILs and counting..._
 - [Assert An Exception Is Raised](elixir/assert-an-exception-is-raised.md)
 - [Binary Representation Of A String](elixir/binary-representation-of-a-string.md)
 - [Check For A Substring Match](elixir/check-for-a-substring-match.md)
+- [Comparing DateTime Structs](elixir/comparing-datetime-structs.md)
 - [Compute md5 Digest Of A String](elixir/compute-md5-digest-of-a-string.md)
 - [Counting Records With Ecto](elixir/counting-records-with-ecto.md)
 - [Create A Date With The Date Sigil](elixir/create-a-date-with-the-date-sigil.md)
diff --git a/elixir/comparing-datetime-structs.md b/elixir/comparing-datetime-structs.md
new file mode 100644
index 0000000..2b40947
--- /dev/null
+++ b/elixir/comparing-datetime-structs.md
@@ -0,0 +1,26 @@
+# Comparing DateTime Structs
+
+> Remember, comparisons in Elixir using ==/2, >/2, </2 and friends are
+> structural and based on the DateTime struct fields. For proper comparison
+> between datetimes, use the compare/2 function.
+
+As the [DateTime docs](https://hexdocs.pm/elixir/DateTime.html) say, you'll
+want to use [`compare/2`](https://hexdocs.pm/elixir/DateTime.html#compare/2)
+in order to accurately compare two `DateTime` structs.
+
+```elixir
+{:ok, older} = DateTime.from_naive(~N[2016-05-24 13:26:08.003], "Etc/UTC")
+{:ok, newer} = DateTime.from_naive(~N[2017-11-24 13:26:08.003], "Etc/UTC")
+
+DateTime.compare(older, newer)
+#=> :lt
+
+DateTime.compare(newer, older)
+#=> :gt
+
+DateTime.compare(newer, newer)
+#=> :eq
+```
+
+When using `compare/2`, you'll get one of `:lt`, `:gt`, or `:eq` as a
+result, meaning _less than_, _greater than_, or _equal_ respectively.