Question

 (** adds an header option in the header option list*)
 let add_headers header key value =
 { header with
   headers = Http_headers.add key value header.headers }

How to understand “header with headers …” ? I guess it “replace” the header.headers with a new headers. Howerver, the passed header should be immutable, shouldnot it ?

Sincerely!

Answer 1

Yes, the passed header is (or can be) immutable. This function doesn’t actually modify its argument; it just returns a copy of it, with the copy’s headers field “replaced”, as you say.