Sinatra Request Object

问题:

I'm probably missing something painfully obvious here, but I can't seem to find an answer, or work it out myself. In Sinatra, they have a self.get method, which captures blocks, when a block is called, you're able to use the request variable inside, how is this possible?

Sinatra

module Sinatra
  class Base
    class Request < Rack::Request   
    end

    attr_accessor :request

    def call!(env)
      @request = Request.new(env)
    end

    class << self
      def get(path, opts = {}, &block)
        ...
      end
    end
  end
end

App

class App < Sinatra::Base
  get '/' do
    puts request
  end
end

回答1:

Wow. You piqued my curiousity, and sure enough, researching this was facinating. The magic starts in the compile! method defined at: https://github.com/sinatra/sinatra/blob/master/lib/sinatra/base.rb#L1529

def compile!(verb, path, block, options = {})
  options.each_pair { |option, args| send(option, *args) }
  method_name = "#{verb} #{path}"
  unbound_method = generate_method(method_name, &block)
  pattern, keys = compile path
  conditions, @conditions = @conditions, []

  wrapper = block.arity != 0 ?
    proc { |a,p| unbound_method.bind(a).call(*p) } :
    proc { |a,p| unbound_method.bind(a).call }
  wrapper.instance_variable_set(:@route_name, method_name)

  [ pattern, keys, conditions, wrapper ]
end

Notice we turn the block passed to get (or any route function) into an unbound method via generate_method (defined a few lines above). We then store a proc which takes two parameters, an object to bind the method to, and a list of arguments, which the method is called with.

Skip ahead to process_route: https://github.com/sinatra/sinatra/blob/master/lib/sinatra/base.rb#L971

def process_route(pattern, keys, conditions, block = nil, values = [])
  route = @request.path_info
  route = '/' if route.empty? and not settings.empty_path_info?
  return unless match = pattern.match(route)
  values += match.captures.to_a.map { |v| force_encoding URI.unescape(v) if v }

  if values.any?
    original, @params = params, params.merge('splat' => [], 'captures' => values)
    keys.zip(values) { |k,v| Array === @params[k] ? @params[k] << v : @params[k] = v if v }
  end

  catch(:pass) do
    conditions.each { |c| throw :pass if c.bind(self).call == false }
    block ? block[self, values] : yield(self, values)
  end
ensure
  @params = original if original
end

Theres a lot going on here, but the key is:

block[self, values]

This calls the stored block above with self, and the appropriate arguments. Thus the unbound method is bound to whatever process_route is bound to( the current self in process_route). And what is process_route bound to? An instance of Sinatra::Base, which as we know has an attribute accessor request that can now be reached in your original block. Tada!