Class: Dry::Monads::Lazy

Inherits:
Task
  • Object
show all
Defined in:
lib/dry/monads/lazy.rb

Overview

Lazy is a twin of Task which is always executed on the current thread. The underlying mechanism provided by concurrent-ruby ensures the given computation is evaluated not more than once (compare with the built-in lazy assignement ||= which does not guarantee this).

Defined Under Namespace

Modules: Mixin

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Task

#==, [], #apply, #bind, #complete?, #discard, failed, #fmap, #initialize, #monad, #or, #or_fmap, pure, #to_maybe, #to_monad, #to_result, #value_or, #wait

Constructor Details

This class inherits a constructor from Dry::Monads::Task

Class Method Details

.new(promise = nil, &block) ⇒ Object 



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# File 'lib/dry/monads/lazy.rb', line 16

def new(promise = nil, &block)
  if promise
    super(promise)
  else
    super(Concurrent::Promise.new(executor: :immediate, &block))
  end
end

Instance Method Details

#evaluated? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/dry/monads/lazy.rb', line 45

def evaluated?
  @promise.complete?
end

#force ⇒ Lazy

Forces the computation. Note that if the computation thrown an error it won't be re-raised as opposed to value!/force!.

Returns:



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# File 'lib/dry/monads/lazy.rb', line 39

def force
  @promise.execute
  self
end

#to_s ⇒ String Also known as: inspect

Returns:

  • (String) 


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# File 'lib/dry/monads/lazy.rb', line 53

def to_s
  state = case promise.state
          when :fulfilled
            value!.inspect
          when :rejected
            "!#{promise.reason.inspect}"
          else
            "?"
          end

  "Lazy(#{state})"
end

#value! ⇒ Object Also known as: force!

Forces the compution and returns its value.

Returns:

  • (Object) 


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# File 'lib/dry/monads/lazy.rb', line 30

def value!
  @promise.execute.value!
end