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Allows flashes to stack intelligently, while preserving existing behavior of the Rails FlashHash


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 Project Readme


  • Allows flashes to stack intelligently like arrays.
  • Follows the principle of least surprise for existing behavior of Rails' FlashHash.
Project Stackable Flash
gem name stackable_flash
license License: MIT
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Stackable Flash overrides the :[]= method of Rails' FlashHash with the result being that each flash key is an array. It is designed following the "Principle of least surprise", so in most ways the flash works as it always has. Only now you can push things onto the array with :<<, and generally interact with the flash as an array. In order to be as compatible as possible with existing implementations of the FlashHash on websites, :[]= will still replace the entire object at that key.


Add this line to your application's Gemfile:

gem 'stackable_flash'

And then execute:

$ bundle

Or install it yourself as:

$ gem install stackable_flash

Config (Optional)

In an environment file, or application.rb

# Here are a few ideas (Don't do them all, pick one):
# You can use a lambda instead of a proc
StackableFlash::Config.configure do
  # Leave it as an array
  config[:stack_with_proc] = Proc.new {|arr| arr }
  # Make a set of statements separated by br tags
  config[:stack_with_proc] = Proc.new {|arr| arr.join('<br/>') }   # THIS IS DEFAULT IF LEFT UNCONFIGURED
  # Make a set of p tags:
  config[:stack_with_proc] = Proc.new {|arr| arr.map! {|x| "<p>#{x}</p>"}.join }
  # Make an unordered list of tags:
  config[:stack_with_proc] = Proc.new {|arr| '<ul>' + arr.map! {|x| "<li>#{x}</li>"}.join + '</ul>' }


When turned on all flashes can be interacted with as arrays.

flash[:notice] = 'First message'              # Will have the same affect that pushing it onto an array would
flash[:notice] << 'Second message'            # No need to initialize first, or test to see if responds to :<<
flash[:notice] |= 'Third message'             # Will add this message only if unique in the stack
flash[:notice] += ['Fourth','Fifth']          # Will add all of the messages onto the stack individually.

flash[:notice] # is now: ['First message','Second message','Third message','Fourth','Fifth']

But StackableFlash preserves existing functionality for code you already have written.

flash[:notice] += ' Appended'                  # Will append a message to the top/last message on the stack.

flash[:notice] # is now: ['First message','Second message','Third message','Fourth','Fifth Appended']

flash[:notice] = 'Overwrite'

flash[:notice] # is now: ['Overwrite']

It is on by default. To turn it off:

StackableFlash.stacked = false

To turn it back on:

StackableFlash.stacked = true

You can even start out with it off set a flash, turn it on, and add to the stack:

StackableFlash.stacked = false
flash[:notice] = 'string'
StackableFlash.stacked = true
flash[:notice] << 'string'

There are block helpers which I am sure some enterprising individual will have a use for:

StackableFlash.stacked do
  flash[:notice] = 'a simple string'  # You can continue to use flash as if this gem did not exist
  flash[:notice] << 'another'         # will stack the strings
  flash[:notice]                      # => ['a simple string','another'],
  # Uses the :stack_with_proc to transform
  flash[:notice].stack                # => "a simple string<br/>another" (default config uses <br/>),
  flash[:notice] = ''                 # will overwrite everything above, and set back to empty string

StackableFlash.stacked({:stack_with_proc => Proc.new {|arr| arr.map! {|x| "<p>#{x}</p>"}.join } } ) do
  flash[:error] = 'original'
  flash[:error] << 'message'
  flash[:error]        # => ['original','message']
  flash[:error].stack  # => '<p>original</p><p>message</p>'


StackableFlash.not_stacked do
  flash[:notice] = 'original'
  flash[:notice] << ' message'
  flash[:notice]        # => 'original message'
  # Uses the :stack_with_proc to transform
  flash[:notice].stack  # => NoMethodError !!!


This gem is used by the cacheable_flash gem to provide stacking flashes. You can check it out for a working example.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
  6. Create new Pull Request


This library aims to adhere to Semantic Versioning 2.0.0. Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency 'stackable_flash', '~> 4.0'


Licensed under the MIT License.