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Dry::Types typedefs found to be generally useful. Replaces deprecated prolog-dry-types.


= 1.15.2
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= 4.6.1
= 5.10.2
= 3.4.2
= 0.10.0
= 12.0.0
= 4.7.1
= 0.49.1
= 0.14.1


= 0.3.1
= 0.11.0
= 2.3.8
 Project Readme


NOTE: This Gem supersedes the previous prolog-dry-types Gem, which suffered from two major problems:

  1. It was tied to the now-obsolete dry-types Gem Release 0.7.2, in a bid to avoid (or at least defer) several breaking changes that were encountered by Prolog applications upgrading to Release 0.8.0. This bit us later when using this Gem in conjunction with other dry-rb Gems and finding that the current docu­mentation and available support no longer matched the code we were using; and
  2. It required that all uses of the root-level Dry or Types namespace modules, conventional in dry-types, be explicitly marked as root-level; e.g., that value objects subclass ::Dry::Types::Value rather than simply Dry::Types::Value.

The document that follows is the README from prolog-dry-types Release 0.3.0, modified only as needed to reflect the change from prolog-dry-types to prolog-dry_types.

This Gem defines some fairly general-purpose types using the dry-types Gem which, for those not familiar with it yet, is the successor to the venerable Virtus Gem, originally created by Piotr Solnica and contributors. As part of the dry-rb collection of Gems, dry-types is an extremely useful tool that quickly becomes habit-forming. Side-effects may include more explicit, therefore more understandable code; increased developer happiness, and decreased baldness. (One of those has yet to be proven in actual use.)

Prolog::DryTypes leverages dry-types, defining several types in the Dry::Types module namespace as documented below under Usage. They can be used individually by your code or all type definitions may be included by requiring 'prolog/dry_types',


Add this line to your application's Gemfile:

gem 'prolog-dry_types'

And then execute:

$ bundle

Or install it yourself as:

$ gem install prolog-dry_types


This Gem uses dry-types to define (currently) four basic data types suitable for declaring attributes in a Dry::Types::Struct (mutable) data structure or a Dry::Types::Value immutable value object. These are Types::Range and its Strict equivalent, Types::Strict::Range; Types::IntegerRange, Types::TimeOrNow, and Types::UUID. Each of these is presented in greater detail below.

Types::Range and Types::Strict::Range

Declared in prolog/dry_types/range.rb

Example usage

# in your `range_demo.rb` file

require 'prolog/dry_types/range' # or 'prolog/dry_types'

class RangeDemo < Dry::Types::Value
  attribute :name, Types::Strict::String
  attribute :range, Types::Strict::Range

# Let's be interactive...

$ pry
[1] pry(main)> require '/path/to/range_demo'
[2] pry(main)> range = name: 'Some Name', range: 2..5
     :name => "Some Name",
    :range => 2..5
[3] pry(main)> range.range.include? 5
[4] exit


The attribute value is a Range instance; it has all the quirks and behaviours that a Range instance declared more "conventionally" would have. In particular, a Range whose lower bound exceeds its upper bound (such as (5..2)) will always be empty. As one would reasonably expect, this attribute may be initialised by either an inclusive (e.g., 0..5) or exclusive (0...5) Range, which respectively includes or excludes the upper bound.


Declared in prolog/dry_types/integer_range.rb

Example usage

# in your 'demo_range.rb' file

require 'prolog/dry_types/integer_range' # or 'prolog/dry_types'

class DemoRange < Dry::Types::Struct
  attribute :name, Types::Strict::String
  attribute range: Types::IntegerRange

# Let's be interactive...
$ pry
[1] pry(main)> require '/path/to/demo_range'
[2] pry(main)> range1 = name: 'A Name', range: nil # defaults to 0..0
     :name => "A Name",
    :range => 0..0
[2] pry(main)> range2 = name: 'Another Name', range: 8
     :name => "Another Name",
    :range => 0..8
[3] pry(main)> range3 = name: 'One More', range: (-1..1)
    :name => "One More",
   :range => -1..1
[4] pry(main)> range3.range.to_a
    [0] -1,
    [1] 0,
    [2] 1
[5] pry(main)> exit


Types::IntegerRange can be used as though it were a Types::Range, with the attribute initialisation using a standard Range instance. It was initially developed, however, to provide an easy shorthand for a Range with a lower bound of zero, for which one only need supply the upper bound.


Declared in prolog/dry_types/time_or_now.rb

Example usage

# In your 'time_demo.rb' file

require 'prolog/dry_types/time_or_now'

class TimeDemo < Dry::Types::Value
  attribute :when, Types::TimeOrNow

# Interactive again
$ pry
[1] pry(main)> require '/path/to/time_demo'
[2] pry(main)> t0 =; t1 = when: nil
    :when => 2016-07-31 01:56:11 +0800
[3] pry(main)> t1.when - t0
1.3e-05                    # 13 microseconds on this system
[4] pry(main)> t2 = when: Time.parse('23 Jan 2016 12:34:56 SGT')
    :when => 2016-01-23 12:34:56 +0800
[5] pry(main)> t3 = when: '23 Jan 2016 12:34:56 SGT'
Dry::Types::StructError: [] "23 Jan 2016 12:34:56 SGT" (String) has invalid type for :when
  from (...omitted...):in 'rescue in new'
[6] pry(main)> exit


This attribute class was originally Types::DateTimeOrNow, wrapping a DateTime instance rather than a Time instance. The change was made in line with recently-updated community coding guidelines which recommend against use of DateTime unless a need exists "to account for historical calendar reform".


Declared in prolog/dry_types/uuid.rb

Example usage

# In your 'uuid_demo.rb' file

require 'prolog/dry_types/uuid'

class UuidDemo < Dry::Types::Value
  attribute :id, Types::UUID

# Once again, interactive demo
$ pry
[1] pry(main)> require '/path/to/uuid_demo'
[2] pry(main)> demo1 = id: nil
    :id => "419c7d80-38b0-0134-4fad-3c0754526993"
[3] pry(main)> puts
[4] pry(main)> demo2 = id: '12345678-1234-5678-123456789012'
    :id => "12345678-1234-5678-4fad-123456789012"
[5] pry(main)> demo3 = id: '12345678123456784fad123456789012'
Dry::Types::StructError: [] "12345678123456784fad123456789012" (String) has invalid type for :id
from (omitted):in 'rescue in new'
[6] pry(main)> exit


Remember that UUIDs, by definition, are for all practical purposes never generated with the same value twice; one common source of grief is to have your test code generate a UUID, then test your code under test which also generates a UUID, and from there, hilarity ensues as you try to figure out why your tests never pass.

Also remember that the only valid format for a UUID is as a string; if you want to work with the value as though it were a vector of bytes, integers, etc, then you are On Your Own with the existing code.


After checking out the repo, run bin/setup to create a Gemfile.lock file which identifies specific versions of runtime and development dependencies of this Gem (which as of now must already be installed on your local system). Then, run bin/rake test to run the tests, or bin/rake to run tests and, if tests are successful, further static-analysis tools (RuboCop, Flay, Flog, and Reek).

To install your build of this Gem onto your local machine, run bin/rake install. We recommend that you uninstall any previously-installed "official" Gem to increase your confidence that your tests are running against your build.


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.