object_space/finalizers_no_parens.rb

tests/_examples/object_space/finalizers_no_parens.rb in the metorex repository.

# Finalizers run as the program ends, including one defined while they run.
class Resource
  def initialize(name)
    @name = name
  end
end

first = Resource.new("first")
handler = proc { |id| puts "first finalized" }
p ObjectSpace.define_finalizer(first, handler) == [0, handler]
# An equal finalizer is kept once, and the one already there is answered.
p ObjectSpace.define_finalizer(first, handler.dup)[1].equal?(handler)

second = Resource.new("second")
ObjectSpace.define_finalizer(second, proc do |id|
  third = Resource.new("third")
  ObjectSpace.define_finalizer(third, proc { |inner| puts "third finalized" })
  puts "second finalized"
end)

# A finalizer that raises is reported, and the others still run.
ObjectSpace.define_finalizer(Resource.new("failing"), proc { |id| raise "finalizing" })

begin
  ObjectSpace.define_finalizer(:name) { }
rescue ArgumentError => error
  p error.message
end
begin
  ObjectSpace.define_finalizer(first, Object.new)
rescue ArgumentError => error
  p error.message
end

Output:

true
true
"cannot define finalizer for Symbol"
"wrong type argument Object (should be callable)"
first finalized
second finalized
third finalized