Why do I get NoMethodError: undefined method `rescue' for #<Concurrent::Future:...>?

Question

Ruby's Concurrent::Future was not catching the exceptions. So I copied the code from an article to add a rescue block. But now I got the error:

Caused by NoMethodError: undefined method `rescue' for #Concurrent::Future:0x0000000124764268

Here is the code:

executed_future = Concurrent::Future.execute do
            url = "#{endpoint}#{datum[:hierarchy_id]}#{valuation_date}"
            raise StandardError.new("Testing error!") # To test

            [...]
          end.rescue do | exception | # Adding this, will throw the error
            @exceptions << exception
            binding.pry # No activated
          end

What am I missing?

I expect to rescue exceptions in the Concurrent::Future block. Just like the article does.

Answer 1

I am not familiar with Concurrent::Future and I might miss a that there exists a different implementation of a rescue method in that specific gem.

But in Ruby rescue is not a method that you call on the return value of another method (like the return value of the Concurrent::Future.execute call in your question). It is a keyword that catches exception raise in the context of the current block.

Therefore, I would try using the idiomatic Ruby begin ... rescue ... end syntax within the Concurrent::Future.execute block:

executed_future = Concurrent::Future.execute do
  begin
    url = "#{endpoint}#{datum[:hierarchy_id]}#{valuation_date}"
    raise StandardError.new("Testing error!") # To test
    # ...
  rescue StandardError => exception
    @exceptions << exception
    binding.pry
  end
end