Thy

Thy is a minimal, strict runtime type system for Ruby.

Motivation

There are many existing runtime type systems for Ruby, most notably, dry-types. Here's why you might prefer Thy:

Thy encourages strictness. Avoiding type coercion as much as possible is an excellent way to keep your code predictable and straightforward.
Minimalism. Thy's API only has what's needed, nothing more.
No Any type. Don't worry, if you have to, you can get it!

Installation

Add this line to your application's Gemfile:

gem 'thy'

And then execute:

$ bundle

Or install it yourself as:

$ gem install thy

Usage

It's recommended not to use Thy directly (although you can), but to create a module for working with types, and to include Thy::Types into it.

module Types
  include Thy::Types
end

To run a type check, call check on a type you need. For example:

module Types
  include Thy::Types
end

Types::String.check('a string').success? # => true
Types::Integer.check(3.14).success?      # => false

If a check fails, a message describing the failure is provided:

Types::String.check(3).failure? # => true
Types::String.check(3).message # => "Expected a String, but got: 3"

Custom types

Thy allows you to define custom types via Thy::Type's constructor:

module Types
  include Thy::Types

  NonZeroValue = Thy::Type.new { |value| value != 0 }
end

Providing meaningful error messages

module Types
  include Thy::Types

  NonZeroValue = Thy::Type.new do |value|
    value != 0 || Thy::Result::Failure.new("Expected #{value.inspect} to be nonzero")
  end
end

Building on top of existing types

Extending existing types is simple, too:

module Types
  include Thy::Types

  NonZeroInteger = Thy.refine_type(Integer, Thy::Type.new { |v| v != 0 })
end

Direct usage

You can use Thy types directly, for example, if you'd like to play around in the console:

Thy::String.check('Bob').success? # => true
PositiveInteger = Thy.refine_type(Integer, Thy::Type.new { |v| v > 0 })

Built-in type reference

Primitive types

# String
Thy::String.check('Bob').success? # => true

# Symbol
Thy::Symbol.check(:bob).success? # => true

# Numeric
Thy::Numeric.check(3.14).success? # => true
Thy::Numeric.check(0).success? # => true

# Float
Thy::Float.check(3.14).success? # => true

# Integer
Thy::Integer.check(3).success? # => true

# Boolean
Thy::Boolean.check(true).success? # => true
Thy::Boolean.check(false).success? # => true

# Time
Thy::Time.check(Time.now).success? # => true
Thy::Time.check(0).success? # => false

# DateTime
require 'date'
Thy::DateTime.check(DateTime.now).success? # => true
Thy::DateTime.check(0).success? # => false

# nil
Thy::Nil.check(nil).success? # => true
Thy::Nil.check(0).success? # => false

Parameterized types

# Array
Thy::Array(Thy::Integer).check([1, 2, 3]).success? # => true
Thy::Array(Thy::String).check(%w[hi hello sup]).success? # => true

# Hash
Thy::Hash({
  name: Thy::String,
  age: Thy::Integer,
}).check({ name: 'Bob', age: 18 }).success? # => true

# Map
Thy::Map(Thy::Symbol, Thy::Integer).check({ a: 1, b: 2 }).success? # => true

# Variant
Thy::Variant(Thy::Integer, Thy::Float).check(3.14).success? # => true
Thy::Variant(Thy::Integer, Thy::Float).check(3).success? # => true

# Enum
Thy::Enum('USD', 'EUR').check('EUR').success? # => true

# Option
Thy::Option(Thy::String).check('a string').success? # => true
Thy::Option(Thy::String).check(nil).success? # => true

# InstanceOf
class A; end
class B < A; end
class C; end
Thy::InstanceOf(A).check(B.new).success? # => true
Thy::InstanceOf(A).check(C.new).success? # => false

# ClassExtending
Thy::ClassExtending(A).check(B).success? # => true
Thy::ClassExtending(A).check(C).success? # => false

Other types

# UntypedArray
Thy::UntypedArray.check(1, 'string', 3.14).success? # => true

# UntypedHash
Thy::UntypedHash.check({ a: 1, b: 'c', 1 => true }).success? # => true

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/akxcv/thy.

License

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

thy

Development

Thy