Add String Interpolation With Instance Variables as a ruby til

Author: jbranchaud

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_427 TILs and counting..._
+_428 TILs and counting..._
 
 ---
 
@@ -333,6 +333,7 @@ _427 TILs and counting..._
 - [Set RVM Default Ruby](ruby/set-rvm-default-ruby.md)
 - [Show Public Methods With Pry](ruby/show-public-methods-with-pry.md)
 - [Squeeze Out The Extra Space](ruby/squeeze-out-the-extra-space.md)
+- [String Interpolation With Instance Variables](ruby/string-interpolation-with-instance-variables.md)
 - [Summing Collections](ruby/summing-collections.md)
 - [Uncaught Exceptions In Pry](ruby/uncaught-exceptions-in-pry.md)
 - [`undef_method` And The Inheritance Hierarchy](ruby/undef-method-and-the-inheritance-hierarchy.md)

ruby/string-interpolation-with-instance-variables.md

@@ -0,0 +1,31 @@
+# String Interpolation With Instance Variables
+
+When using regular variables with string interpolation in Ruby, they must be
+wrapped in curly braces (e.g. `"This is a #{variable}"`). With instance
+variables (and class and global variables) you can just use the _octothorp_
+followed directly by the variable.
+
+Here is an example of this in action:
+
+```ruby
+class Person
+  def initialize(name)
+    @name = name
+  end
+
+  def whoami
+    puts "I am #@name"
+  end
+end
+
+bob = Person.new("bob")
+#=> #<Person:0x007fdaf3291618 @name="bob">
+
+bob.whoami
+# I am bob
+```
+
+This is a handy shortcut, but may affect readability and/or result in an
+interpolation error at some point. Your mileage may vary.
+
+h/t Josh Davey