Ruby方法可选参数和&block参数

Question

1. Hey there

   Is it possible to have optional attributes and a block as parameters for a method call?

   Example: I have to call

   method(foo, foo: bar, -> { do_something }
   

   and tried it with

   def method(foo, *bar, &block)
   end
   

   As for my understanding the block always has to be at last position?

   After a bit of research I found out the unary(?) * seems to be for arrays. Since I try to pass a Hash I changed the code to

   def method(foo, bar={}, &block)
   end
   

   But this doesn't do the trick either. I guess its because he cant figure out where the bar ends and the block starts.

   Any ideas or suggestions? Thank you in advance

   Append: Just for the curious why I need this. We have a big json schema running and have a small DSL that builds the json from the model definitation. Without going to much into detail we wanted to implement exportable_scopes.

   class FooBar
     exportable_scope :some_scope, title: 'Some Scope', -> { rewhere archived: true }
   end
   

   On some initializer this is supposed to happens:

   def exportable_scope scope, attributes, &block
     scope scope block
     if attributes.any?
       attributes.each do |attribute|
         exportable_schema.scopes[scope] = attribute
       end
     else
       exportable_schema.scopes[scope] = {title: scope}
     end
   end
   

   So this is working fine, I just need a hint for the method parameters.

- Denny Mueller

---

我认为，您可以使用exportable_scope(:some_scope, title: 'Some Scope'){ rewhere archived: true }。您不需要像参数一样发送块。 - Lukas Baliak

我认为你混淆了传递块和将可调用对象(lambda)作为参数传递，这是ActiveRecord .scope期望接收的。范围的主体是必需的，因此您可以将方法签名更改为exportable_scope(name, body, attributes = {})并调用scope name, body。在这里查看.scope定义：https://github.com/rails/rails/blob/dc925119a3912ecfe0df400007163f33b99d6385/activerecord/lib/active_record/scoping/named.rb#L143。`exportable_scope :some_scope, -> { rewhere archived: true }, title: 'Some Scope'`。 - Alexandre Angelim

Answer 1

是的，这是可能的。

当混合不同类型的参数时，它们必须按照以下特定顺序包含在方法定义中：

1. 位置参数（必需和可选）和单个splat参数，任意顺序；
2. 关键字参数（必需和可选），任意顺序；
3. 双星号参数；
4. 块参数（前缀为&）；

上面的顺序有一定的灵活性。我们可以定义一个方法并以一个单独的splat参数开始参数列表，然后是几个可选位置参数，等等。虽然Ruby允许这样做，但通常这是一个非常糟糕的实践，因为代码会很难读懂，甚至更难调试。通常最好使用以下顺序：

1. 必填位置参数；
2. 可选位置参数（具有默认值）；
3. 单个splat参数；
4. 关键字参数（必需和可选，其顺序无关紧要）；
5. 双星号参数；
6. 显式块参数（前缀为&）。

例如：

def meditate cushion, meditation="kinhin", *room_items, time: , posture: "kekkafuza", **periods, &b
    puts "We are practicing #{meditation}, for #{time} minutes, in the #{posture} posture (ouch, my knees!)."
    puts "Room items: #{room_items}"
    puts "Periods: #{periods}"
    b.call # Run the proc received through the &b parameter
end

meditate("zafu", "zazen", "zabuton", "incense", time: 40, period1: "morning", period2: "afternoon" ) { puts "Hello from inside the block" }

# Output:
We are practicing zazen, for 40 minutes, in the kekkafuza posture (ouch, my knees!).
Room items: ["zabuton", "incense"]
Periods: {:period1=>"morning", :period2=>"afternoon"}
Hello from inside the block

请注意，在调用该方法时，我们做了以下几个操作：

• 提供了必需的位置参数cushion；
• 覆盖了可选的位置参数meditation的默认值；
• 通过*room_items参数传递了额外的位置参数(zabuton和incense)；
• 提供了必需的关键字参数time；
• 省略了可选的关键字参数posture；
• 通过**periods参数传递了额外的关键字参数(period1: "morning", period2: "afternoon")；
• 通过&b参数传递了代码块{ puts "Hello from inside the block" }。

请注意，上面的示例仅用于说明可以混合使用不同类型的参数。在实际代码中构建这样的方法是不好的实践。如果一个方法需要那么多参数，最好将其拆分为更小的方法。如果绝对需要向单个方法传递这么多数据，我们应该考虑创建一个类来更有组织地存储数据，然后将该类的实例作为单个参数传递给该方法。

- BrunoF