hashing

Hashing

Gives you an easy way to specify which instances vars of your objects should be used as key => value to serialize it into a hash returned by the #to_h method. Also gives you a YourClass::from_hash to reconstruct the instances.

Status

Installation

Add this line to your application's Gemfile:

gem 'hashing'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hashing

Contact

• API Doc: http://rdoc.info/gems/hashing
• Bugs, issues and feature requests: https://github.com/ricardovaleriano/hashing/issues
• Support: http://stackoverflow.com/questions/tagged/hashing-ruby

Usage

Given a File class like this:

class File
  def initialize(path, commit = nil, content = nil)
    @path, @commit, @content = path, commit, content
  end
end

And I want to turn instances of it in a Hash like the one below, so I can, for example, turn this Hash into a YAML to save it in a file.

{
  path: @path,
  commit: @commit,
  content: @content
}

I just need to include the Hashing module, and then indicates which instance vars (ivars) should be used in the serialization using the class method hasherize:

class File
  include Hashing
  hasherize :path, :commit, :content
end

#to_h

Then I will be able to call the #to_h method in any instance of File to obtain the "hasherized®" version of it:

file = File.new 'README.md', 'cfe9aacbc02528b', '#Hashing\n\nWow. Such code...'

file.to_h
# {
#   path: 'README.md',
#   commit: 'cfe9aacbc02528b',
#   content: '#Hashing\n\nWow. Such code...'
# }

::from_hash

And I can tell Hashing how one can create an instance of File given a valid Hash like the one created by a #to_h call:

class File
  include Hashing
  hasherize(:path, :commit, :content).
    loading ->(hash) { new hash[:path], hash[:commit], hash[:content] }

  # ...
end

So I can transform instances of any Ruby class into hashes and rebuild objects of any type from hashes, accordingly with my business rules, without expose these rules outside my classes.

Note that both #to_h and ::from_hash methods are public, and you can and should call them whatever you need in your programs. But the ::from_hash method will be called by Hashing when building your instances from hashes (more about this: nested hasherizing).

Custom "hasherizing" and loading strategies

Many times you will need apply some computation over the contents of your ivars transform them in a primitive that can be stored as a Hash.

Following the File class example, maybe you want to store the @content as a Base64 enconded string.

Hashing allows you to specify the strategy of serialization and loading when indicating which ivars should be part of the final Hash:

require 'base64'

class File
  include Hashing

  hasherize :path, :commit

  hasherize(:content).
    to(->(content) { Base64.encode64 content }).
    from(->(content_string) { Base64.decode64 content_string }).
    loading ->(hash) { new hash[:path], hash[:commit], hash[:content] }

  # ...
end

But I will recomend this approach only if your strategy for serialization is more complex than just call a method in an object passing the raw value. If your need is exactly like this, you can just indicate the object and the methods that should be called in what moment:

require 'base64'

class File
  include Hashing

  hasherize(:path, :commit).
    loading ->(hash) { new hash[:path], hash[:commit], hash[:content] }

  hasherize(:content).using(Base64).to(:encode64).from(:decode64)

  # ...
end

And finally, if the your serialization logic is worth a method on it's own, you can indicate this by passing the method names via symbol to the :to and :from options. Since those methods don't necessarily make sense as part of your public api, so you can even make then private:

require 'base64'

class File
  include Hashing

  hasherize(:path, :commit).
    loading ->(hash) { new hash[:path], hash[:commit], hash[:content] }

  hasherize(:content).to(:encode).from(:decode)

  # ...

  private
  def encode(content)
    Base64.encode64 content
  end

  def decode(content)
    Base64.decode64 content
  end

  # ...
end

Custom hasherizing and loading strategies for multiple ivars

You can indicate the same strategies for hasherzing and load from hashes for multiple ivars if it makes sense to your program:

class File
  include Hashing

  hasherize(:path, :commit).
    to(->(value) { value.downcase }).
    from(->(value) { value.upcase })
end

This will guarantees that the final Hash has the path and the commit values "downcased" when your object is serialized, and "upcased" when the instance is reconstructed.

Nested hasherized objects

But if your transformations are a little more complicated than a simple Base64 encoding, chances are there that you have a nested objects to be serialized.

Extending our example, maybe our File class have an internal collection of Annotation, to allow the user to indicate what is in which line of a file:

# annotation.rb

class Annotation
  include Hasherize.new :lines, :annotation

  def initialize(lines, annotation)
    @lines = lines
    @annotation = annotation
  end
end

And the File class could have a method to add new annotations:

# file.rb

class File
  # ...

  def annotate(lines, annotation)
    @annotations ||= []
    @annotations << Annotation.new(lines, annotation)
  end
  # ...
end

So in this case, if you wants a file to be hasherized® with it's internall @annotations preserved, you just indicate this in the File class. The example now can be rewritten as:

class File
  include Hashing

  hasherize :path, :commit
  hasherize(:annotations).collection Annotation

  # ...
end

Since the Annotation class has it's own notion of #to_h and ::from_hash, this is all that Hashing needs to build a File instances from a valid Hash.

Defining attr_reader within the .hasherize invocation

If you want to define readers for the ivars passed to .hasherize, you can do this with the option attr: true (defaults to false).

So, the following example:

class File
  include Hashing
  hasherize :path, :commit, :content

  attr_reader :path, :commit, :content
end

Can be written as:

class File
  include Hashing
  hasherize(:path, :commit, :content).reader true
end

Contributing

This is a rapid "scratch your own itch" kind of project. It will make me really happy if it can be used used in your software anyhow. If you need something different than what is in it, or can solve us some bugs or add documentation, it will be very well received!

Here is how you can help this gem:

• Fork it ( https://github.com/ricardovaleriano/hashing/fork )
• Create your feature branch (git checkout -b my-new-feature)
• Commit your changes (git commit -am 'Add some feature')
• Push to the branch (git push origin my-new-feature)
• Create a new Pull Request