Add Refer To Implicit Block Argument With It 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).
 
-_1554 TILs and counting..._
+_1555 TILs and counting..._
 
 ---
 
@@ -1303,6 +1303,7 @@ _1554 TILs and counting..._
 - [Question Mark Operator](ruby/question-mark-operator.md)
 - [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)
 - [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)

ruby/refer-to-implicit-block-argument-with-it.md

@@ -0,0 +1,43 @@
+# Refer To Implicit Block Argument With It
+
+One of the key features of the Ruby 3.4 release is the `it` implicit block
+argument.
+
+The vast majority of inline blocks defined in Ruby code receive a single block
+argument. Typically we name and reference a block argument explictly like so:
+
+```ruby
+items.map { |item| item * item }
+```
+
+Ruby likes to cut away excess syntax when possible. To that end, the implicit
+`it` block argument has been added. This is an identifier we can reference in
+the context of a block and its value is the current
+
+```ruby
+items = [1,2,3,4,5]
+
+squares = items.map { it * it }
+
+pp squares
+#=> [1, 4, 9, 16, 25]
+```
+
+Note: we cannot mix numbered parameters (`_1`, `_2`) with the `it` parameter.
+If we do, we'll get the following error:
+
+```ruby
+def method_using_block(a, b)
+  yield(a, b) if block_given?
+end
+
+puts method_using_block(4,5) { _2 ** _1 } #=> 625
+puts method_using_block(4,5) { _2 ** it }
+# it_block.rb:12: syntax error found (SyntaxError)
+#   10 |
+#   11 | puts method_using_block(4,5) { _2 ** _1 }
+# > 12 | ... it }
+#      |     ^~ `it` is not allowed when a numbered parameter is already used
+```
+
+[source](https://docs.ruby-lang.org/en/3.4/NEWS_md.html)