class Functional::Delay
Lazy evaluation of a block yielding an immutable result. Useful for expensive operations that may never be needed.
When a ‘Delay` is created its state is set to `pending`. The value and reason are both `nil`. The first time the `#value` method is called the enclosed opration will be run and the calling thread will block. Other threads attempting to call `#value` will block as well. Once the operation is complete the value will be set to the result of the operation or the reason will be set to the raised exception, as appropriate. All threads blocked on `#value` will return. Subsequent calls to `#value` will immediately return the cached value. The operation will only be run once. This means that any side effects created by the operation will only happen once as well.
@!macro thread_safe_immutable_object
@see clojuredocs.org/clojure_core/clojure.core/delay Clojure delay
Public Class Methods
Create a new ‘Delay` in the `:pending` state.
@yield the delayed operation to perform
@raise [ArgumentError] if no block is given
# File lib/functional/delay.rb, line 29 def initialize(&block) raise ArgumentError.new('no block given') unless block_given? super synchronize do @state = :pending @task = block end end
Public Instance Methods
Has the delay been fulfilled? @return [Boolean]
# File lib/functional/delay.rb, line 73 def fulfilled? synchronize{ @state == :fulfilled } end
Is delay completion still pending? @return [Boolean]
# File lib/functional/delay.rb, line 87 def pending? synchronize{ @state == :pending } end
The exception raised when processing the block. Returns ‘nil` if the operation is still `:pending` or has been `:fulfilled`.
@return [StandardError] the exception raised when processing the block
else nil.
# File lib/functional/delay.rb, line 50 def reason synchronize{ @reason } end
Has the delay been rejected? @return [Boolean]
# File lib/functional/delay.rb, line 80 def rejected? synchronize{ @state == :rejected } end
Current state of block processing.
@return [Symbol] the current state of block processing
# File lib/functional/delay.rb, line 41 def state synchronize{ @state } end
Return the (possibly memoized) value of the delayed operation.
If the state is ‘:pending` then the calling thread will block while the operation is performed. All other threads simultaneously calling `#value` will block as well. Once the operation is complete (either `:fulfilled` or `:rejected`) all waiting threads will unblock and the new value will be returned.
If the state is not ‘:pending` when `#value` is called the (possibly memoized) value will be returned without blocking and without performing the operation again.
@return [Object] the (possibly memoized) result of the block operation
# File lib/functional/delay.rb, line 67 def value synchronize{ execute_task_once } end
Protected Instance Methods
@!visibility private
Execute the enclosed task then cache and return the result if the current state is pending. Otherwise, return the cached result.
@return [Object] the result of the block operation
# File lib/functional/delay.rb, line 99 def execute_task_once if @state == :pending begin @value = @task.call @state = :fulfilled rescue => ex @reason = ex @state = :rejected end end @value end