Bug (?) by using ResponseTrait within a filter

Is it right, that some things, if used in the constructor, not work as expected?

It does not work as expected.
Because the constructor cannot return a Response object.
Controller should return a Response object.

And in a filter, what you do is just return the Response object that you want.
See https://codeigniter4.github.io/CodeIgnit...ponse.html

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