Do not modify queue name in place. Create a new String

[douglasmiller]

I regularly include the magic comment, # frozen_string_literal: true, in my ruby code.

This results in an error when defining a queue_name in a consumer class, since the Hutch::Broker class will modify the string instead of creating a new one: lib/hutch/broker.rb:177:in 'prepend': can't modify frozen String (FrozenError)

[michaelklishin]

Thank you!