Module: DataMapper::Sweatshop::Unique

Included in:
DataMapper::Sweatshop
Defined in:
lib/dm-sweatshop/unique.rb

Defined Under Namespace

Classes: TooManyTriesException

Instance Method Summary collapse

Instance Method Details

#unique(key = nil, &block) ⇒ Object

Yields a value to the block. The value is unique for each invocation with the same block. Alternatively, you may provide an explicit key to identify the block.

If a block with no parameter is supplied, unique keeps track of previous invocations, and will continue yielding until a unique value is generated. If a unique value is not generated after @UniqueWorker::MAX_TRIES@, an exception is raised.

ParseTree is required unless an explicit key is provided

(1..3).collect { unique {|x| x }}     # => [0, 1, 2]
(1..3).collect { unique {|x| x + 1 }} # => [1, 2, 3]
(1..3).collect { unique {|x| x }}     # => [3, 4, 5] # Continued on from above
(1..3).collect { unique(:a) {|x| x }} # => [0, 1, 2] # Explicit key overrides block identity

a = [1, 1, 1, 2, 2, 3]
(1..3).collect { unique { a.shift }}  # => [1, 2, 3]
(1..3).collect { unique { 1 }}        # raises TooManyTriesException

return <Object> the return value of the block



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# File 'lib/dm-sweatshop/unique.rb', line 27

def unique(key = nil, &block)
  if block.arity < 1
    UniqueWorker.unique_map ||= {}

    key ||= UniqueWorker.key_for(&block)
    set = UniqueWorker.unique_map[key] || Set.new
    result = block[]
    tries = 0
    while set.include?(result)
      result = block[]
      tries += 1

      raise TooManyTriesException.new("Could not generate unique value after #{tries} attempts") if tries >= UniqueWorker::MAX_TRIES
    end
    set << result
    UniqueWorker.unique_map[key] = set
  else
    UniqueWorker.count_map ||= Hash.new() { 0 }

    key ||= UniqueWorker.key_for(&block)
    result = block[UniqueWorker.count_map[key]]
    UniqueWorker.count_map[key] += 1
  end

  result
end