Add Construct A Constant From A String as a ruby til.

README.md

@@ -118,6 +118,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Are They All True?](ruby/are-they-all-true.md)
 - [Assoc For Hashes](ruby/assoc-for-hashes.md)
 - [Comparing Class Hierarchy Relationships](ruby/comparing-class-hierarchy-relationships.md)
+- [Construct A Constant From A String](ruby/construct-a-constant-from-a-string.md)
 - [Create an Array of Stringed Numbers](ruby/create-an-array-of-stringed-numbers.md)
 - [Destructuring Arrays In Blocks](ruby/destructuring-arrays-in-blocks.md)
 - [Disassemble Some Codes](ruby/disassemble-some-codes.md)

ruby/construct-a-constant-from-a-string.md

@@ -0,0 +1,28 @@
+# Construct A Constant From A String
+
+Ruby's
+[`Module.const_get`](http://ruby-doc.org/core-2.1.0/Module.html#method-i-const_get)
+can be used to look for and retrieve the constant for the given name.
+
+This can be used to construct a class name
+
+```ruby
+> Object.const_get("Math")
+#=> Math
+> Object.const_get("Math")::PI
+#=> 3.141592653589793
+```
+
+It can also be used to reference a constant
+
+```ruby
+> Object.const_get("Math::PI")
+#=> 3.141592653589793
+```
+
+You can even be more specific if you'd like
+
+```ruby
+> Math.const_get("PI")
+#=> 3.141592653589793
+```