Add OpenStruct Has Bad Performance Characteristics as a Ruby TIL

ruby/open-struct-has-bad-performance-characteristics.md

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+# OpenStruct Has Bad Performance Characteristics
+
+The Ruby docs for `OpenStruct` have a [_Caveats_
+section](https://ruby-doc.org/3.4.1/stdlibs/ostruct/OpenStruct.html#class-OpenStruct-label-Caveats)
+that warns about the poor performance characteristics of `OpenStruct` relative
+to `Struct` and `Hash`.
+
+> This should be a consideration if there is a concern about the performance of
+> the objects that are created, as there is much more overhead in the setting
+> of these properties compared to using a Hash or a Struct. Creating an open
+> struct from a small Hash and accessing a few of the entries can be 200 times
+> slower than accessing the hash directly.
+
+This doesn't mean don't use `OpenStruct`, but do be aware of if you are using
+it in a hot path or if you are allocating and processing tons of them.
+
+If you turn on _Performance Warnings_ in Ruby, you'll see a warning message
+when allocating an `OpenStruct`.
+
+```ruby
+> require 'ostruct'
+=> true
+> os1 = OpenStruct.new
+=> #<OpenStruct>
+> Warning[:performance] = true
+=> true
+> os2 = OpenStruct.new
+(irb):6: warning: OpenStruct use is discouraged for performance reasons
+=> #<OpenStruct>
+```
+
+[source](https://www.reddit.com/r/ruby/comments/1d54mwl/comment/l6jgn59/)