Use immutable types in a few more places

[tysmith]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.61%. Comparing base (430ce35) to head (ffc9284).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #480   +/-   ##
=======================================
  Coverage   99.61%   99.61%           
=======================================
  Files          56       56           
  Lines        5655     5655           
=======================================
  Hits         5633     5633           
  Misses         22       22           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.