class ActionDispatch::Flash::FlashHash

def self.from_session_value(value) #:nodoc:

:nodoc: 
def self.from_session_value(value) #:nodoc:
  case value
  when FlashHash # Rails 3.1, 3.2
    flashes = value.instance_variable_get(:@flashes)
    if discard = value.instance_variable_get(:@used)
      flashes.except!(*discard)
    end
    new(flashes, flashes.keys)
  when Hash # Rails 4.0
    flashes = value["flashes"]
    if discard = value["discard"]
      flashes.except!(*discard)
    end
    new(flashes, flashes.keys)
  else
    new
  end
end

def [](k) 

def [](k)
  @flashes[k.to_s]
end

def []=(k, v) 

def []=(k, v)
  k = k.to_s
  @discard.delete k
  @flashes[k] = v
end

def alert

Convenience accessor for flash[:alert]. 
def alert
  self[:alert]
end

def alert=(message)

Convenience accessor for flash[:alert]=. 
def alert=(message)
  self[:alert] = message
end

def clear 

def clear
  @discard.clear
  @flashes.clear
end

def delete(key) 

def delete(key)
  key = key.to_s
  @discard.delete key
  @flashes.delete key
  self
end

def discard(k = nil)

flash.discard(:warning) # discard only the "warning" entry at the end of the current action
flash.discard # discard the entire flash at the end of the current action

Marks the entire flash or a single flash entry to be discarded by the end of the current action: 
def discard(k = nil)
  k = k.to_s if k
  @discard.merge Array(k || keys)
  k ? self[k] : self
end

def each(&block) 

def each(&block)
  @flashes.each(&block)
end

def empty? 

def empty?
  @flashes.empty?
end

def initialize(flashes = {}, discard = []) #:nodoc:

:nodoc: 
def initialize(flashes = {}, discard = []) #:nodoc:
  @discard = Set.new(stringify_array(discard))
  @flashes = flashes.stringify_keys
  @now     = nil
end

def initialize_copy(other) 

def initialize_copy(other)
  if other.now_is_loaded?
    @now = other.now.dup
    @now.flash = self
  end
  super
end

def keep(k = nil)

flash.keep(:notice) # keeps only the "notice" entry, the rest of the flash is discarded
flash.keep # keeps the entire flash

Keeps either the entire current flash or a specific flash entry available for the next action: 
def keep(k = nil)
  k = k.to_s if k
  @discard.subtract Array(k || keys)
  k ? self[k] : self
end

def key?(name) 

def key?(name)
  @flashes.key? name.to_s
end

def keys 

def keys
  @flashes.keys
end

def notice

Convenience accessor for flash[:notice]. 
def notice
  self[:notice]
end

def notice=(message)

Convenience accessor for flash[:notice]=. 
def notice=(message)
  self[:notice] = message
end

def now

# Equivalent to flash.now[:notice] = "Good luck now!"
flash.now.notice = "Good luck now!"

# Equivalent to flash.now[:alert] = "Beware now!"
flash.now.alert = "Beware now!"

Also, brings two convenience accessors:

Entries set via now are accessed the same way as standard entries: flash['my-key'].

vanish when the current action is done.
When you need to pass an object to the current action, you use now, and your object will
When you need to pass an object to the next action, you use the standard flash assign ([]=).
This method enables you to use the flash as a central messaging system in your app.

flash.now[:message] = "Hello current action"

Sets a flash that will not be available to the next action, only to the current. 
def now
  @now ||= FlashNow.new(self)
end

def now_is_loaded? 

def now_is_loaded?
  @now
end

def replace(h) #:nodoc:

:nodoc: 
def replace(h) #:nodoc:
  @discard.clear
  @flashes.replace h.stringify_keys
  self
end

def stringify_array(array) # :doc:

:doc: 
def stringify_array(array) # :doc:
  array.map do |item|
    item.kind_of?(Symbol) ? item.to_s : item
  end
end

def sweep #:nodoc:

:nodoc:
This method is called automatically by filters, so you generally don't need to care about it.

Mark for removal entries that were kept, and delete unkept ones. 
def sweep #:nodoc:
  @discard.each { |k| @flashes.delete k }
  @discard.replace @flashes.keys
end

def to_hash 

def to_hash
  @flashes.dup
end

def to_session_value #:nodoc:

:nodoc:
If there are none to keep, returns +nil+.
Builds a hash containing the flashes to keep for the next request. 
def to_session_value #:nodoc:
  flashes_to_keep = @flashes.except(*@discard)
  return nil if flashes_to_keep.empty?
  { "discard" => [], "flashes" => flashes_to_keep }
end

def update(h) #:nodoc:

:nodoc: 
def update(h) #:nodoc:
  @discard.subtract stringify_array(h.keys)
  @flashes.update h.stringify_keys
  self
end