Add Reference Hash Key With Safe Navigation as a Ruby TIL

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).
 
-_1681 TILs and counting..._
+_1683 TILs and counting..._
 
 See some of the other learning resources I work on:
 
@@ -710,6 +710,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Keyboard Shortcuts For Interesting With Text Areas](mac/keyboard-shortcuts-for-interacting-with-text-areas.md)
 - [List All The Say Voices](mac/list-all-the-say-voices.md)
 - [Open Finder.app To Specific Directory](mac/open-finder-app-to-specific-directory.md)
+- [Prevent Sleep With The Caffeinate Command](mac/prevent-sleep-with-the-caffeinate-command.md)
 - [Quickly Type En Dashes And Em Dashes](mac/quickly-type-en-dashes-and-em-dashes.md)
 - [Require Additional JS Libraries In Postman](mac/require-additional-js-libraries-in-postman.md)
 - [Resize App Windows With AppleScript](mac/resize-app-windows-with-applescript.md)
@@ -1419,6 +1420,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Rake Only Lists Tasks With Descriptions](ruby/rake-only-lists-tasks-with-descriptions.md)
 - [Read The First Line From A File](ruby/read-the-first-line-from-a-file.md)
 - [Refer To Implicit Block Argument With It](ruby/refer-to-implicit-block-argument-with-it.md)
+- [Reference Hash Key With Safe Navigation](ruby/reference-hash-key-with-safe-navigation.md)
 - [Rendering ERB](ruby/rendering-erb.md)
 - [Replace The Current Process With An External Command](ruby/replace-the-current-process-with-an-external-command.md)
 - [Require Entire Gemfile In Pry Session](ruby/require-entire-gemfile-in-pry-session.md)

mac/prevent-sleep-with-the-caffeinate-command.md

@@ -0,0 +1,30 @@
+# Prevent Sleep With The Caffeinate Command
+
+MacOS has a built-in utility `caffeinate` that can programatically prevent your
+machine from sleeping. There are two kinds of sleep that it can prevent via
+_assertions_.
+
+> caffeinate creates assertions to alter system sleep behavior.
+
+The two kinds of sleep behavior are _display sleep_ and _system idle sleep_. An
+assertion to prevent display sleep can be created with `-d` and system idle
+sleep with `-i`.
+
+We can combine those to prevent both and then specify a duration (_timeout_)
+with `-t` (with a value in seconds).
+
+```bash
+caffeinate -d -i -t 600
+```
+
+This creates assertions with 10 minute timeouts for both display and system idle
+sleep.
+
+The `caffeinate` command is blocking, so if you want to start it in the
+background, you can do that like so:
+
+```bash
+caffeinate -d -i -t 600 &
+```
+
+See `man caffeinate` for more details.

ruby/reference-hash-key-with-safe-navigation.md

@@ -0,0 +1,30 @@
+# Reference Hash Key With Safe Navigation
+
+Let's say we have a variable that we expect to be a hash, but could also be
+`nil`. We want to try to grab a value from that hash by referencing a specific
+key. Because it could be `nil`, we cannot simply do:
+
+```ruby
+stuff[:key]
+```
+
+As that could result in `NoMethodError: undefined method '[]' for nil
+(NoMethodError)`.
+
+We should use the _safe navigation_ operator (`&`) to avoid raising that error.
+However, we should pay attention to a necessary syntax shift from the short-hand
+`[:key]` to the long-hand `[](:key)`.
+
+```ruby
+stuff&.[](:key)
+```
+
+The meaning of this syntax is that we are calling the `#[]` method and we pass
+it a single argument `:key` wrapped in parentheses.
+
+Another approach would be to use `#dig` which can feel more ergonomic than the
+above syntax switch.
+
+```ruby
+stuff&.dig(:key)
+```