Ruby 2.3 preparedness

[AaronLasseigne]

With 2.3 around the corner we need to make sure the code works. Right now all tests pass in 2.3 (run locally) and I don't see anything that should cause us problems. We need to make sure 2.3 is added to our Travis CI runs when it becomes available.

Ruby 2.3 is introducing a pragma to make all strings immutable by default. The though is that by Ruby 3 this will be standard. It works by adding # frozen_string_literal: true to the top of the file. Then all strings created using single or double quotes are immutable. If you need a mutable string it will need to be created using String.new.

I would like to adopt the new pragma so that people using 2.3 can get the performance benefit and we're ready for Ruby 3 ahead of time. @tfausak thoughts?

[AaronLasseigne]

One thing to consider is that we need to make sure the string coming back from a string filter is mutable. That would be an unexpected surprise for people.

[tfausak]

Instead of adding the pragma, why don't we .freeze all our literal strings? That way previous versions would get frozen strings and we would accidentally give frozen strings back to the user.

[tfausak]

On second thought, freezing every string is going to be super annoying. They are created in a variety of ways that are hard to grep for. You've got normal string literals, which can be delimited with ' or '" or % and friends, and then you've got string array literals, which can be %w and friends. And then you've got things that happen to return strings, like to_s and inspect. I'd rather let the magic comment take care of things.

That being said, I think we should benchmark our codebase against 2.3 with and without frozen strings. It might not make much of a difference.