紅寶石爲無返回undefined方法+：nilClass

Question

運行下面的代碼：

# experiment 
time = 5000 
# when time reaches 10000, I'm off duty 
def speedup_time(incre) 
    time += incre 
    yield(time) 
end 

puts "is the day over yet? #{speedup_time(2000){ 
    if incre >= 10000 
    "yes: #{time}" 
    else 
    "no: #{time}" 
    end 
}}" 

我就遇到了這個錯誤：undefined method "+" for nil:nilClass。

Answer 1

time變量超出範圍（Ruby中的定義方法具有自己的作用域，並且看不到任何外部變量）。試試這個：

# when time reaches 10000, I'm off duty 
def speedup_time(incre) 
    time = 5000 
    time += incre 
    yield(time) 
end 

而你的第二個表達錯誤。我想應該是這樣的：

speed_var = speedup_time(2000) do |time| 
    if time >= 10000 
    "yes: #{time}" 
    else 
    "no: #{time}" 
    end 
end 
puts "is the day over yet? #{speed_var}" 

或短三元運算符：

speed_var = speedup_time(2000) { |time| (time >= 10000) ? "yes: #{time}" : "no: #{time}" } 
puts "is the day over yet? #{speed_var}" 

或：

puts %Q|is the day over yet? #{speedup_time(2000){ |time| (time >= 10000) ? "yes: #{time}" : "no: #{time}"}}| 

Answer 2

I was thinking of using the yield and adapt this to a promise.then style as I was accustomed to in javascript, is there a way to adapt this with yield.

你將要學習塊多一點因爲這也不起作用：

def do_stuff(x) 
    yield 
end 


do_stuff(10) { puts x } 


--output:-- 
2.rb:6:in `block in <main>': undefined local variable or method `x' for main:Object (NameError) 
    from 2.rb:2:in `do_stuff' 
    from 2.rb:6:in `<main>' 

很明顯，當涉及到紅寶石範圍時，你會迷失方向。獲得一個開始紅寶石書。閱讀。 Ruby不是JavaScript。

#----A def creates a new scope--+ 
def do_stuff    # | 
    x = 10     # | 
end      # | 
#-------------------------------+ 
#...which means nothing inside that box can see anything outside the box 
#except for constants, which are visible everywhere 

y = 20 

p = Proc.new do #Proc.new and lambda create anonymous functions in ruby 
    puts y 
    puts x 
    puts z 
end 

def test(p) 
    z = 30 
    p.call #execute proc, can also be written as p[] 
end 

test p 

玩弄這個例子，註釋掉各種puts語句。