Built-in boolean support

[maxlinc]

When I wrote the support for coercing primitive types, I wrote:

Hashie does not have built-in support for coercion boolean values, since Ruby does not have a built-in boolean type or standard method for to a boolean. You can coerce to booleans using a custom proc.

Although that's true there is a boolean standard for json and a slightly less strict standard for yaml. I think those should be common enough that it might make sense to ship an implementation that handles validation/coercion for one or both standards.

So rather than the proc currently in the README:

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :retweeted, ->(v) do
    case v
    when String
      return !!(v =~ /^(true|t|yes|y|1)$/i)
    when Numeric
      return !v.to_i.zero?
    else
      return v == true
    end
  end
end

You could do:

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :retweeted, Hashie::Boolean # or perhaps Hashie::JSON::Boolean or Hashie::YAML::Boolean
end

This isn't equivalent to the sample proc, but its similar and more standard. For example, the YAML standard doesn't coerce numerics.

[dblock]

I would be down with this.

[mkcode]

I did this in my application, leveraging ActiveModel:

class ProfileData < Hashie::Dash
  include Hashie::Extensions::Dash::Coercion

  class Boolean
    def self.coerce(value)
      ::ActiveModel::Type::Boolean.new.cast(value)
    end
  end

  property :is_admin, coerce: Boolean

  ...
end

Although this is actually a non-trivial issue. If you reference different libraries, you will find varied behavior.

See ActiveModel:

class Boolean < Value
  FALSE_VALUES = [false, 0, "0", "f", "F", "false", "FALSE", "off", "OFF"].to_set

  def cast_value(value)
    if value == ""
      nil
    else
      !FALSE_VALUES.include?(value)
    end
  end

Defined here: https://github.com/rails/rails/blob/159b774887cfb3d5c862b2b48d24d75b658e47af/activemodel/lib/active_model/type/boolean.rb

Now check out dry-types - another very well done type library:

module Dry
  module Types
    module Coercions
      module Form
        TRUE_VALUES = %w[1 on On ON t true True TRUE T y yes Yes YES].freeze
        FALSE_VALUES = %w[0 off Off OFF f false False FALSE F n no No NO].freeze
        BOOLEAN_MAP = ::Hash[TRUE_VALUES.product([true]) + FALSE_VALUES.product([false])].freeze
...

Defined here: https://github.com/dry-rb/dry-types/blob/6fa7aff1257cddc2e46e3f022db4d2fa6bde318f/lib/dry/types/coercions/form.rb#L8-L10

Very different behavior between these two. ActiveModel returns nil only for empty string, false for the above FALSE_VALUES and true for EVERYTHING else. Dry-types returns true and false for the strings with the TRUE/FALSE_VALUES, and nil for everything else.

If this was up to me - we would totally redo to coercion system, with a thin wrapper to provide compatibility with the type library of your choosing. ActiveModel::Type and Dry::Types would be a great start. Note that Dry::Types gets you far more fine grained control over your types: http://dry-rb.org/gems/dry-types/built-in-types/

[dblock]

@mkcode That makes sense and is certainly ambitious, but who dares wins!

[mkcode]

@dblock - Are you the maintainer for this project? I may take a stab at creating a PR for this - I'd love to be able to use Dry::Type with Hashie since I use it elsewhere in one one of my applications. I would want to get your input on how to implement this, or what you think the API should be in order to enable this.

For example:

We could switch the type system based off the availability of gems with a predefined priority. Like use Dry::Types if it is available, otherwise use ActiveModel::Type if it is available, or otherwise use the current builtin coercion. This may break backwards compatibility if someone upgrades though.

Or we could create a class level option?

class ProfileData < Hashie::Dash
  coercion_class :active_model
  include Hashie::Extensions::Dash::Coercion
  ...
end

Explicit module names?:

class ProfileData < Hashie::Dash
  include Hashie::Extensions::Dash::Coercion::ActiveModel
  ...
end

I think I would prefer an option to the included coercion module, like so:

class ProfileData < Hashie::Dash
  include Hashie::Extensions::Dash::Coercion(:active_model)
  ...
end

Please instruct!

[dblock]

@mkcode I am. One of. Trying to. Along with some other lovely people. I have the glorious merge/release privileges ;)

[dblock]

I prefer the very explicit method that defaults to the old way, aka exactly what you said @mkcode. Give it a try!