Ruby-on-rails 仅在存在时调用方法
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Call method only if it exists
提问by Frans
Is there some hidden Ruby/Rails-magic for simply calling a method only if it exists?
是否有一些隐藏的 Ruby/Rails-magic 仅在方法存在时才调用它？
Lets say I want to call
假设我想打电话
resource.phone_number
but I don't know beforehand if resource responds to phone_number. A way to do this is
但我事先不知道资源是否响应phone_number. 一种方法是
resource.phone_number if resource.respond_to? :phone_number
That's not all that pretty if used in the wrong place. I'm curious if something exists that works more along the lines of how tryis used (resource.try(:phone_number)).
如果在错误的地方使用，那并不是那么漂亮。我很好奇是否存在更符合try使用方式的东西（resource.try(:phone_number)）。
采纳答案by Aleksei Matiushkin
If you are not satisfied with the standard ruby syntax for that, you are free to:
如果您对标准的 ruby 语法不满意，您可以自由地：
class Object
def try_outside_rails(meth, *args, &cb)
self.send(meth.to_sym, *args, &cb) if self.respond_to?(meth.to_sym)
end
end
Now:
现在：
resource.try_outside_rails(:phone_number)
will behave as you wanted.
会如你所愿。
回答by jmarceli
I would try defined?(http://ruby-doc.org/docs/keywords/1.9/Object.html#defined-3F-method). It seems to do exactly what you are asking for:
我会尝试defined?（http://ruby-doc.org/docs/keywords/1.9/Object.html#defined-3F-method）。它似乎完全符合您的要求：
resource.phone_number if defined? resource.phone_number
回答by Bhavya
I know this is very old post. But just wanted to know if this could be a possible answer and whether the impact is the same .
我知道这是很老的帖子。但只是想知道这是否是一个可能的答案以及影响是否相同。
resource.try(:phone_number) rescue nil
Thanks
谢谢
回答by Stephen
I can't speak for the efficiency, but something like...
我不能说效率，但像......
Klass.methods.include?(:method_name)
works for me in Rails 4
在 Rails 4 中对我来说有效
回答by nroose
If A.cis defined and A.aand A.bare not, you can do A.a rescue A.b rescue A.cand it will work like a charm. You will be breaking some silly rules, though.
如果A.c被定义，A.a并且A.b都没有，你可以做A.a rescue A.b rescue A.c，它会像一个魅力。不过，您将违反一些愚蠢的规则。
