An uncomfortably common problem when developing for a particular programming language is needing to deal with compatibility issues across different versions of the language runtime. Most often this means keeping individual projects tied to their then-current version of the language until such time that the project can address any compatibility issues with later language releases. To that end, Ruby developers are probably familiar with one of rbenv, chruby or rvm, for example. Elixir isn’t much different in this regard.