Using a param inside of a spawn doesn't work

[jwoertink]

This code:

class SomeAction < BrowserAction
  param code : String

  get "/some-action" do
    spawn { puts code }
    head 201
  end
end

results in this error at runtime:

Unhandled exception in spawn:                                                                                  
Closed stream (IO::Error)                                                                                      
  from /usr/local/Cellar/crystal/0.26.1/src/io.cr:128:5 in 'check_open'                                        
  from /usr/local/Cellar/crystal/0.26.1/src/io/memory.cr:219:5 in 'gets_to_end'                                
  from lib/lucky/src/lucky/params.cr:303:5 in 'body'                                                           
  from lib/lucky/src/lucky/params.cr:240:23 in 'form_params'                                                   
  from lib/lucky/src/lucky/params.cr:223:7 in 'body_param'                                                     
  from lib/lucky/src/lucky/params.cr:47:32 in 'get?'                                                           
  from src/actions/some_action.cr:2:3 in 'code'                                                         
  from src/actions/some_action.cr:4:3 in '->'                                                                   
  from /usr/local/Cellar/crystal/0.26.1/src/fiber.cr:255:3 in 'run'                                            
  from /usr/local/Cellar/crystal/0.26.1/src/fiber.cr:29:34 in '->'

I assume this has something to do with the param method being lazy evaluated or something. So when it's in the other thread, calling that code method calls in to the IO that no longer exists.

This is easily solved by doing

  get "/some-action" do
    c = code
    spawn { puts c }
    head 201
  end

However, maybe this is an easy fix? Or maybe a prettier error message like ParameterException?