從塊返回 - 從塊內調用的方法？

Question

我想在Ruby中的塊中指定規則（在這個例子中，規則定義是「好」還是「壞」）的DSL。下面是一個（非常簡化的版本），我想做的事：

def test_block 
    # Lots of other code 
    is_good = yield # ... should give me true or false 
    # Lots of other code 
end 

test_block do 
    good if some_condition 
    good if some_other_condition 
    bad 
end 

有什麼辦法，我可以定義方法good和bad，使該塊休息時間嗎？在上面的例子中，我想：

• 檢查，如果some_condition是真實的，如果是，打出來的塊，並將它返回true
• 檢查，如果some_other_condition是真實的，如果是這樣，打出來的塊，並將它返回true
• 回報從塊假無條件如果我們仍然在它

即我要讓上面的代碼的行爲，就好像我有writt恩，像這樣的塊：

result = test_block do 
    break true if some_condition 
    break true if some_other_condition 
    break false 
end 

在好/壞方法的定義把break顯然是行不通的。有沒有其他方法可以達到我想要的效果，還是應該考慮採取一些完全不同的方法來實現這一目標？

Answer 1

您可以在塊中引發異常並捕獲該異常。

module Tester 
    class Breaker < Exception; end 
    class GoodBreak < Breaker; end 
    class BaadBreak < Breaker; end 
end 

def test_block(name) 
    begin 
    yield 
    rescue Tester::Breaker=>e 
    case e 
     when Tester::GoodBreak then puts "All is well with #{name}" 
     when Tester::BaadBreak then puts "BAD STUFF WITH #{name}" 
     else raise 
    end 
    end 
end 

def good; raise Tester::GoodBreak; end 
def bad; raise Tester::BaadBreak; end 

test_block('early out') do 
    good if true 
    good if puts("NEVER SEE THIS") || true 
    bad 
end 

test_block('simple pass') do 
    good if false 
    good if puts("SEE THIS FROM PASS TEST") || true 
    bad 
end 

test_block('final fail') do 
    good if false 
    good if puts("SEE THIS BUT PUTS IS NIL") 
    bad 
end 

#=> All is well with early out 
#=> SEE THIS FROM PASS TEST 
#=> All is well with simple pass 
#=> SEE THIS BUT PUTS IS NIL 
#=> BAD STUFF WITH final fail 

下面是使用throw/catch另一個例子，而不是raise/rescue（更新通過沿返回值）（感謝@jleedev！）：

def test_block(name) 
    result = catch(:good){ catch(:bad){ yield } } 
    puts "Testing #{name} yielded '#{result}'", "" 
end 

def good; throw :good, :good; end 
def bad; throw :bad, :bad; end 

test_block('early out') do 
    good if true 
    good if puts("NEVER SEE THIS") || true 
    bad 
end 

test_block('simple pass') do 
    good if false 
    good if puts("SEE THIS FROM PASS TEST") || true 
    bad 
end 

test_block('final fail') do 
    good if false 
    good if puts("SEE THIS BUT PUTS IS NIL") 
    bad 
end 

#=> Testing early out yielded 'good' 
#=> 
#=> SEE THIS FROM PASS TEST 
#=> Testing simple pass yielded 'good' 
#=> 
#=> SEE THIS BUT PUTS IS NIL 
#=> Testing final fail yielded 'bad'