Introduction

dry-types is a simple and extendable type system for Ruby; useful for value coercions, applying constraints, defining complex structs or value objects and more. It was created as a successor to Virtus.

Example usage

require 'dry-types'
require 'dry-struct'

module Types
  include Dry.Types()
end

User = Dry.Struct(name: Types::String, age: Types::Integer)

User.new(name: 'Bob', age: 35)
# => #<User name="Bob" age=35>

See Built-in Types for a full list of available types.

By themselves, the basic type definitions like Types::String and Types::Integer don't do anything except provide documentation about which type an attribute is expected to have. However, there are many more advanced possibilities:

Strict types will raise an error if passed an attribute of the wrong type:

class User < Dry::Struct
  attribute :name, Types::Strict::String
  attribute :age,  Types::Strict::Integer
end

User.new(name: 'Bob', age: '18')
# => Dry::Struct::Error: [User.new] "18" (String) has invalid type for :age

Coercible types will attempt to convert an attribute to the correct class
using Ruby's built-in coercion methods:

class User < Dry::Struct
  attribute :name, Types::Coercible::String
  attribute :age,  Types::Coercible::Integer
end

User.new(name: 'Bob', age: '18')
# => #<User name="Bob" age=18>
User.new(name: 'Bob', age: 'not coercible')
# => ArgumentError: invalid value for Integer(): "not coercible"

Use .optional to denote that an attribute can be nil (see Optional Values):

class User < Dry::Struct
  attribute :name, Types::String
  attribute :age,  Types::Integer.optional
end

User.new(name: 'Bob', age: nil)
# => #<User name="Bob" age=nil>
# name is not optional:
User.new(name: nil, age: 18)
# => Dry::Struct::Error: [User.new] nil (NilClass) has invalid type for :name
# keys must still be present:
User.new(name: 'Bob')
# => Dry::Struct::Error: [User.new] :age is missing in Hash input

Add custom constraints (see Constraints):

class User < Dry::Struct
  attribute :name, Types::Strict::String
  attribute :age,  Types::Strict::Integer.constrained(gteq: 18)
end

User.new(name: 'Bob', age: 17)
# => Dry::Struct::Error: [User.new] 17 (Fixnum) has invalid type for :age

Add custom metadata to a type:

class User < Dry::Struct
  attribute :name, Types::String
  attribute :age,  Types::Integer.meta(info: 'extra info about age')
end

User.schema.key(:age).meta
# => {:info=>"extra info about age"}

Pass values directly to Dry::Types without creating an object using []:

Types::Strict::String["foo"]
# => "foo"
Types::Strict::String["10000"]
# => "10000"
Types::Coercible::String[10000]
# => "10000"
Types::Strict::String[10000]
# Dry::Types::ConstraintError: 1000 violates constraints

Features

Support for constrained types
Support for optional values
Support for default values
Support for sum types
Support for enums
Support for hash type with type schemas
Support for array type with members
Support for arbitrary meta information
Support for typed struct objects via dry-struct
Types are categorized, which is especially important for optimized and dedicated coercion logic
Types are composable and reusable objects
No const-missing magic and complicated const lookups
Roughly 6-10 x faster than Virtus

Use cases

dry-types is suitable for many use-cases, for example:

Value coercions
Processing arrays
Processing hashes with explicit schemas
Defining various domain-specific information shared between multiple parts of your application
Annotating objects

Other gems using dry-types

dry-types is often used as a low-level abstraction. The following gems use it already:

TOC

Example usage

Features

Use cases

Other gems using dry-types