What is the difference between `[]=` and `add` for HTTP::Server::Response#headers?

Question

I looked at the source code for both []= and .add when adding/manipulating headers. I'm still confused as to the reason why there are two ways to add/set headers. What are the differences between the two methods?

Answer 1

[]= replaces all header key content with a new array of value

puts response.headers["Accept-Language"] # => ["de"]
response.headers["Accept-Language"] = "de-CH" # or ["de-CH"]
puts response.headers["Accept-Language"] # => ["de-CH"]

.add checks if header key exist and append the value:

puts response.headers["Accept-Language"] # => ["de"]
response.headers.add "Accept-Language", "de-CH"
puts response.headers["Accept-Language"] # => ["de", "de-CH"]