Crystal parallel jobs from an array

parraleln.cr

def paralleln(items : Indexable(T), &block : T -> R) forall T, R
  results = Array(R).new(items.size) { r = uninitialized R }
  done = Channel(Exception?).new

  items.each_with_index do |item, i|
    spawn do
      begin
        results[i] = block.call(item)
      rescue e
        done.send e
      else
        done.send nil
      end
    end
  end

  items.each do
    if (exc = done.receive)
      raise exc
    end
  end

  results
end


require "http/client"

urls = ["https://example.com/", "https://crystal-lang.org"]
pages = paralleln(urls) do |url|
  HTTP::Client.get(url)
end
p pages