dry-types 1.0

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Type Attributes

Types themselves have optional attributes you can apply to get further functionality.

Append .optional to a Type to allow nil

By default, nil values raise an error:

Types::Strict::String[nil]
# => raises Dry::Types::ConstraintError

Add .optional and nil values become valid:

optional_string = Types::Strict::String.optional

optional_string[nil]
# => nil
optional_string['something']
# => "something"
optional_string[123]
# raises Dry::Types::ConstraintError

Types::String.optional is just syntactic sugar for Types::Strict::Nil | Types::Strict::String.

Handle optional values using Monads

The dry-monads gem provides another approach to handling optional values by returning a Monad object. This allows you to pass your type to a Maybe(x) block that only executes if x returns Some or None.

NOTE: Requires the dry-monads gem to be loaded.

  1. Load the :maybe extension in your application.

    require 'dry-types'

Dry::Types.load_extensions(:maybe)
module Types
  include Dry.Types()
end

  2. Append .maybe to a Type to return a Monad object 

x = Types::Maybe::Strict::Integer[nil]
Maybe(x) { puts(x) }

x = Types::Maybe::Coercible::String[nil]
Maybe(x) { puts(x) }

x = Types::Maybe::Strict::Integer[123]
Maybe(x) { puts(x) }

x = Types::Maybe::Strict::String[123]
Maybe(x) { puts(x) }

Types::Maybe::Strict::Integer[nil] # None
Types::Maybe::Strict::Integer[123] # Some(123)

Types::Maybe::Coercible::Float[nil] # None
Types::Maybe::Coercible::Float['12.3'] # Some(12.3)

# 'Maybe' types can also accessed by calling '.maybe' on a regular type:
Types::Strict::Integer.maybe # equivalent to Types::Maybe::Strict::Integer

You can define your own optional types:

maybe_string = Types::Strict::String.maybe

maybe_string[nil]
# => None

maybe_string[nil].fmap(&:upcase)
# => None

maybe_string['something']
# => Some('something')

maybe_string['something'].fmap(&:upcase)
# => Some('SOMETHING')

maybe_string['something'].fmap(&:upcase).value_or('NOTHING')
# => "SOMETHING"

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