how to pass a block to a function as a parameter

Question

I'd like to refactor the following code:

case @request.path
when '/'
  Rack::Response.new do |response|
    do_stuff
  end
when '/env' then Rack::Response.new(@env.to_html)
end

And extract Rack::Response.new, something like the following:

Rack::Response.new case @request.path
when '/'    then Proc.new {|response| do_stuff }
when '/env' then @env.to_html
end

But I get

stringable or iterable required

What's the correct implementation (Ruby 1.9.2)?

Answer 1

Essentially, you are wanting Ruby Procs to be first-class. By design, this language prefers other ways to accomplish your objective.

I see Rack::Response.new's first argument is the response body.

Looking at Rack::Response, you can do something like:

rr = Rack::Response.new
body = ''
block = Proc.new {}

case @request.path
when '/'
  block = Proc.new {|response| do_stuff }
when '/env'
  body = @env.to_html
end

rr.write body
rr.finish &block

Wrapping up rr, block and body into whatever object you wish would improve this further.

Answer 2

In order to pass a block to a function, you need to prefix it with an ampersand.

block_or_string = case @request.path
  when '/'    then Proc.new { |response| do_stuff }
  when '/env' then @end.to_html
end

response = if block_or_string.is_a?(Proc)
  Rack::Response.new(&block_or_string)
else
  Rack::Response.new(block_or_string)
end

This is pretty ugly. It might be an improvement to wrap the strings in simple procs.

block = case @request.path
  when '/'    then Proc.new { |response| do_stuff }
  when '/env' then Proc.new { @end.to_html }
end

Rack::Response.new(&block)