what does this syntax mean in Ruby? .. tasks.all?(&:complete?) [duplicate]

Question

I'm walking through the example project in the Rails 5 Test Prescriptions - Build a Healthy Codebase (published date: 2018) book and encountering this method:

#pages 29-30 of the book
class Project
  .
  .
  def done?
    tasks.all?(&:complete?) #only this line confused me, especially the `&` part
  end
end

the syntax looks really strange to me since I just learned Ruby & Rails for more than one month..any hints just for pointing me to where I should read would be really appreciated

Answer 1

& is for passing block to method as a block (also used the other way in parameter list to make implicit block a parameter), it implicitly calls to_proc on passed object.

Symbol#to_proc for :symbol makes a proc{|param| param.symbol }

So your code is equvalent to tasks.all?{|task| task.complete? }