You're seeing just the function update-exclamation-mark, go back to Attributes module for more information.
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update!(module, path, lambda)

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Updates attribute in path and raise error if not found.

Available at compile time only. It is the extension of update/3 that requires the value and the path to be defined:

  • path should exist
  • value should not be nil


Attributes.update!(MyModule, [:path], :value)