在Ruby中，我应该使用|| =还是定义它?为了记忆? [英] In Ruby, should I use ||= or if defined? for memoization?

问题描述

我应该使用if defined?

 return @current_user_session if defined?(@current_user_session)
 @current_user_session = UserSession.find

或||=

@current_user_session ||= UserSession.find

我注意到if defined?方法被越来越多地使用.一个相对于另一个有什么优势吗?就个人而言，我更喜欢||=的可读性.我还认为Rails可能具有memoize宏，该宏可以透明地提供此行为.是这样吗?

I noticed the if defined? method being used more and more recently. Is there any advantage to one over the other? Personally, I prefer ||= for readability. I also think Rails might have a memoize macro which provides this behavior transparently. Is this the case?

推荐答案

注意:x || = y如果x返回false，则将x = y赋值.这可能意味着x是undefined，nil或false.

Be careful: x ||= y assigns x = y if x returns false. That may mean that x is undefined, nil, or false.

虽然在@current_user_session实例变量的上下文中可能并非如此，但变量会被多次定义和为假.

There are many times variables will be defined and false, though perhaps not in the context of the @current_user_session instance variable.

如果您希望简明扼要，请尝试使用条件构造:

If you desire conciseness, try the conditional construct:

defined?(@current_user_session) ?
    @current_user_session : @current_user_session = UserSession.find

或者只是:

defined?(@current_user_session) || @current_user_session = UserSession.find

如果您只需要初始化变量.

if you just need to initialize the variable.

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