option.cr

Crystal implementation of Scala's Option Monad

Installation

Add this to your application's shard.yml:

dependencies:
  option:
    github: marceloboeira/option.cr

Global

By requiring the library you add the following functions/classes to your global scope

Functions

• none - Creates an instance of the None(Nil) class
• some(value) - Creates an instance of the Some(T) class with the value type. e.g.: some("foo") -> Some(String)
• option(value) - Returns either a None or a Some(T) instance

Classes

• Option(T) - Abstract class that defines the contract followed by None(T)/Some(T)
• None(T) - Class that defines the interaction with nil values
• Some(T) - Class that defines the interaction with the value

Interaction

• get - Returns the value or raises an exception in case of nil
• or_else(default) - Returns the value or the defined default
• empty? - Returns true when the value is not nil, false when is nil

Usage

option("value") #<Some(String):0x10de55bc0 @value="value">
option(123) #<Some(Int32):0x10de5ef10 @value=123>
option(nil) #<None(Nil):0x10de5ef00>

option("123").or_else("0") # "123"
option(nil).or_else("0") # "0"

Examples

require "option"

module UnsafeIO
  class User
    def count : Int32?
      # IO operation can fail
      [10, nil].sample
    end
  end
end

10.times do
  users = option(UnsafeIO::User.new.count).or_else(0)
  puts "#{users} on storage"
end

Check the examples folder for more.