Ruby开发技巧

jieforest

Another use for this would be adapter classes for two disparate services (say database clients for example), mapping the various errors to the same categories, so your rescues still work after you switch out the client under the adapters.

This technique does however come with a drawback. The #extend call will invalidate Ruby’s global method cache, slowing your app for a moment each time it’s called. We will be getting more fine-grained method cache invalidation in Ruby 2.1, at which point there’s nothing to worry about. But even now this can be a very useful and powerful technique.

Modules

Modules serve a number of purposes in Ruby. Perhaps the most visible is as the name-spacing mechanism, and then there is their main intended use as ‘mixins’. Modules like Enumerable and Comparable are fantastic, easily allowing you to add complex behaviour to your classes by defining just a few methods and including the modules. Modules have some other uses too.

jieforest

Sometimes you have a bunch of related methods that are much closer to functions, they take and input, return an output, and don’t do anything with self. Modules act as great way to group these methods together.

Here’s one from one of our apps (there are a couple more methods, but they’re a bit too specific to share).

1. module Geo
   
2.   module_function
   
3. 
   
4.   RADIUS_OF_THE_EARTH = 6371
   
5. 
   
6.   def distance((origin_lat, origin_long), (dest_lat, dest_long))
   
7.     return unless origin_lat && origin_long && dest_lat && dest_long
   
8. 
   
9.     sin_lats = Math.sin(rad(origin_lat)) * Math.sin(rad(dest_lat))
   
10.     cos_lats = Math.cos(rad(origin_lat)) * Math.cos(rad(dest_lat))
    
11.     cos_longs = Math.cos(rad(dest_long) - rad(origin_long))
    
12. 
    
13.     x = sin_lats + (cos_lats * cos_longs)
    
14.     x = [x, 1.0].min
    
15.     x = [x, -1.0].max
    
16. 
    
17.     Math.acos(x) * RADIUS_OF_THE_EARTH
    
18.   end
    
19. 
    
20.   def rad(degree)
    
21.     degree.to_f / (180 / Math::PI)
    
22.   end
    
23. 
    
24.   def degree(rad)
    
25.     rad.to_f * (180 / Math::PI)
    
26.   end
    
27. 
    
28.   def miles(km)
    
29.     km / 1.609344
    
30.   end
    
31. 
    
32.   def km(miles)
    
33.     miles * 1.609344
    
34.   end
    
35. end
    

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jieforest

The module_function declaration at the start of the module is a method visibility modifier, like public, private, orprotected.

It makes the method available directly on the module like a class method, and as a private instance method so the method is available un-prefixed when the module is included.

1. Geo.distance([51.47872, -0.610248], [51.5073346 , -0.1276831])   #=> 33.55959095208182
   
2. 
   
3. include Geo
   
4. distance([51.47872, -0.610248], [51.5073346 , -0.1276831])       #=> 33.55959095208182
   
5. A similar effect can be achieved switching module_fuction to extend self.
   
6. module Geo
   
7.   extend self
   
8.   ...
   
9. end
   

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jieforest

Here the instance methods of the module are copied as class methods. The difference is that you can use the other method visibility modifiers, making methods that are private on the module, or public on the instance (where they would have all been public on the module and private on the instance with module_fuction).

Modules also make for handy singleton objects with no need to mess about preventing more than one copy being instantiated or working out how to get ahold of the reference, it’s all built in to Ruby.

1. require "net/http"
   
2. module APIClient
   
3.   @http = Net:HTTP.new("example.com", 80)
   
4.   @user = "user"
   
5.   @pass = "pass"
   
6. 
   
7.   def self.get(path)
   
8.     request = Net::HTTP::Get.new(path)
   
9.     request.basic_auth(@user, @pass)
   
10.     @http.request
    
11.   end
    
12. end
    
13. 
    
14. response = APIClient.get("/api/examples")
    

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henghu_bai

都是英文，写的还是抄的。