foo.rb

File.open("foo", "w+") {|f| f.puts "bar"}
File.open("foo", "w+") {|f| f.read } #=> queria "bar", mas retorna ""


# API que eu quero


resolver.with_file do |file|
  file.write 'bar'
end # => 3


resolver.with_file do |file|
  file.read
end # => "bar"


#---
resolver.with_file do |_, file|
  file.write 'bar'
end