Ruby-on-rails Rails 验证：if => Proc.new 还是 lambda？
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Rails validation :if => Proc.new or lambda?
提问by Xiaotian Guo
I have found that in all examples (include rails documentation) that I have seen for the :if option of validation methods uses Proc.new instead of lambda, for example
我发现在所有示例（包括 rails 文档）中，我看到的 :if 验证方法选项使用 Proc.new 而不是 lambda，例如
class Foo < ActiveRecord::Base
validates_presence_of :name, :if => Proc.new{|f| .... } # why not lambda here?
end
is there any reason for this? As far as I know, lambda
有什么原因吗？据我所知，拉姆达
- Is more strict with arguments.
- Also return statement in lambda block returns from the block, not from calling function.
- 对参数更严格。
- lambda 块中的 return 语句也从块中返回，而不是从调用函数中返回。
Both seems to be desirable behavior for :if option mentioned above, is there anything I am missing?
两者似乎都是理想的行为：如果上面提到的选项，有什么我遗漏的吗？
回答by Jits
Both seems to be desirable behavior for :if option mentioned above, is there anything I am missing?
两者似乎都是理想的行为：如果上面提到的选项，有什么我遗漏的吗？
I'm guessing that:
我猜是：
It's more desirable to allow Procs as they don't care about the number of arguments. So I could easily write any of the below:
允许 Procs 更可取，因为它们不关心参数的数量。所以我可以轻松地编写以下任何内容：
validates_presence_of :name, :if => Proc.new{|f| f.display_name.blank? } # I care about 'f' here as I need it to check something.
... and:
... 和：
validates_presence_of :secret_sauce, :if => Proc.new{ MyApp::REQUIRE_SECRET_SAUCE } # I don't care about any arguments being passed in.
This may seem like a minor thing, but I guess it adds to the flexibility.
这似乎是一件小事，但我想它增加了灵活性。
