class Rack::Headers

the downcasing of keys.
(by using non-lowercase response header keys), automatically handling
to be used by rack applications that don’t implement the Rack 3 SPEC
Rack::Headers is a Hash subclass that downcases all keys. It’s designed

def self.[](*items) 

def self.[](*items)
  if items.length % 2 != 0
    if items.length == 1 && items.first.is_a?(Hash)
      new.merge!(items.first)
    else
      raise ArgumentError, "odd number of arguments for Rack::Headers"
    end
  else
    hash = new
    loop do
      break if items.length == 0
      key = items.shift
      value = items.shift
      hash[key] = value
    end
    hash
  end
end

def [](key) 

def [](key)
  super(downcase_key(key))
end

def []=(key, value) 

def []=(key, value)
  super(key.downcase.freeze, value)
end

def assoc(key) 

def assoc(key)
  super(downcase_key(key))
end

def compare_by_identity 

def compare_by_identity
  raise TypeError, "Rack::Headers cannot compare by identity, use regular Hash"
end

def delete(key) 

def delete(key)
  super(downcase_key(key))
end

def dig(key, *a) 

def dig(key, *a)
  super(downcase_key(key), *a)
end

def downcase_key(key) 

def downcase_key(key)
  key.is_a?(String) ? key.downcase : key
end

def except(*a)

:nocov: 
def except(*a)
  super(*a.map!{|key| downcase_key(key)})
end

def fetch(key, *default, &block) 

def fetch(key, *default, &block)
  key = downcase_key(key)
  super
end

def fetch_values(*a) 

def fetch_values(*a)
  super(*a.map!{|key| downcase_key(key)})
end

def has_key?(key) 

def has_key?(key)
  super(downcase_key(key))
end

def invert 

def invert
  hash = self.class.new
  each{|key, value| hash[value] = key}
  hash
end

def merge(hash, &block) 

def merge(hash, &block)
  dup.merge!(hash, &block)
end

def reject(&block) 

def reject(&block)
  hash = dup
  hash.reject!(&block)
  hash
end

def replace(hash) 

def replace(hash)
  clear
  update(hash)
end

def select(&block) 

def select(&block)
  hash = dup
  hash.select!(&block)
  hash
end

def slice(*a)

:nocov: 
def slice(*a)
  h = self.class.new
  a.each{|k| h[k] = self[k] if has_key?(k)}
  h
end

def to_proc 

def to_proc
  lambda{|x| self[x]}
end

def transform_keys(&block) 

def transform_keys(&block)
  dup.transform_keys!(&block)
end

def transform_keys! 

def transform_keys!
  hash = self.class.new
  each do |k, v|
    hash[yield k] = v
  end
  replace(hash)
end

def transform_values(&block) 

def transform_values(&block)
  dup.transform_values!(&block)
end

def update(hash, &block) 

def update(hash, &block)
  hash.each do |key, value|
    self[key] = if block_given? && include?(key)
      block.call(key, self[key], value)
    else
      value
    end
  end
  self
end

def values_at(*keys) 

def values_at(*keys)
  keys.map{|key| self[key]}
end