具有“定义的”的三进制表达返回“表达式”而不是价值？ [英] Ternary expression with "defined?" returns "expression" instead of value?

问题描述

我很喜欢Ruby和Rails，但即使在搜索堆栈溢出和google之后，我也找不到答案。

我有一个简单的Ruby简写if语句应该返回一个整数像这样：

  ＃在这个erb文件的上下文中，amount被定义为5. 
 @c =（定义？amount？amount：r（1,4））
  pre> 
 
 
  r（）是一个自定义帮助函数，在这种情况下返回之间的随机数 1和4。
 
 
 
我打算这样工作的方式是 if  金额被定义，然后使用定义为金额的数量， else 生成一个随机数字在1到4之间，并使用它。
 
 
 
当打印出 @c 但是Ruby输出表达式而不是一个数字。
 
 
 
我要做什么来让这个工作按照我的意图，我做错了什么？ 
 
 
 
非常感谢您阅读！
解决方案
 定义？是否绑定到金额？金额：r（1,4）所以相当于：
 金额：r（1,4））
  
你可能想要：
 定义？（金额）？金额：r（1,4）
  
其实，赔率是 amount | | r（1,4）或 amount.nil？ ？ r（1,4）：amount 会更好地匹配你想要的，因为我认为你不想要这样：
 
 1.9.3p194：001>定义？（金额）
 => nil 
 1.9.3p194：002> amount = nil 
 => nil 
 1.9.3p194： 003>定义？（金额）
 =>局部变量
 
 ...在这种情况下 @c 将是 nil   - 定义变量的值。
 
I'm pretty new to Ruby and Rails but even after searching stack overflow and google I couldn't find an answer to this.

I've got a simple Ruby shorthand if statement that should return an integer like so:
# in the context of this erb document `amount` is defined as 5.
@c = ( defined? amount ? amount : r( 1,4 ) )
r() is a custom helper function that returns a random number between in this case 1 and 4.

The way I intend this to work is that if amount is defined, then use the number defined as amount, else generate a random number between 1 and 4 and use that instead.

When printing out @c however Ruby outputs expression rather than a number.

What do I have to do to get this working as I intended and what am I doing wrong?

Many thanks for reading!
解决方案
defined? is binding to amount ? amount : r(1,4) so it is equivalent to:
defined?(amount ? amount : r(1,4))
You probably want:
defined?(amount) ? amount : r(1,4)
Actually, odds are that amount || r(1,4), or amount.nil? ? r(1,4) : amount would better match what you want, since I think you don't want this:
1.9.3p194 :001 > defined?(amount)
 => nil 
1.9.3p194 :002 > amount = nil
 => nil 
1.9.3p194 :003 > defined?(amount)
 => "local-variable" 
...in which case @c would be nil - the value of the defined variable.

                        
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