What is a gem? And how does OpenStudio use them?

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from here it seems like it [a gem] is just a portable bit of reusable code, is this a sort of correct understanding?

• Yes.

1) Does it matter if a typical user knows any of this to make use of existing capabilities of OS or the BCL?

• No. Normal users don't need to know anything about gems.

2) Do all BCL measures use gems? And, if not, which do and which do not and why?

• Only the Create Baseline Building and Create DOE Prototype Building currently use a gem. The reason is that these measures are very complex and share a lot of code. In order to make this code maintainable, we put it into a single library, which in Ruby is called a gem.

3) are there any gems (or other parts of the OS ecosystem) that need to be updated outside of the regular updates (again, for your run of the mill OS energy modeller)

• No. The gem that these measures use is already installed with OpenStudio, you don't need to do anything besides installing OpenStudio.

4) Are there any OS specific resources for learning about gems and how OS makes use of them?

• Normal users will never have to know about or use gems. Unless you plan on writing a series of very complicated measures which all share a bunch of code, you can ignore gems.