Tyyppi.Struct.update

You're seeing just the function update, go back to Tyyppi.Struct module for more information.
Link to this function

update(target, key, fun)

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Specs

update(target :: struct, key :: atom(), updater :: (any() -> any())) ::
  {:ok, struct} | {:error, any()}
when struct: %{__struct__: atom()}

Updates the value in target under specified key, if passes validation