make eventType a private variables inside

[viney-shih]

No description provided.

[codecov]

Codecov Report

Merging #8 (0a6dba1) into master (bbe6347) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master       #8   +/-   ##
=======================================
  Coverage   88.33%   88.33%           
=======================================
  Files          11       11           
  Lines         540      540           
=======================================
  Hits          477      477           
  Misses         35       35           
  Partials       28       28           

Impacted Files	Coverage Δ
event.go	76.47% <100.00%> (ø)
event_enum.go	100.00% <100.00%> (ø)
factory.go	97.77% <100.00%> (ø)

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