在 Ruby 中，如何检查方法“foo=()"是否正确?被定义为? [英] In Ruby, how do I check if method "foo=()" is defined?

问题描述

在 Ruby 中，我可以定义一个方法 foo=(bar):

In Ruby, I can define a method foo=(bar):

irb(main):001:0> def foo=(bar)
irb(main):002:1>   p "foo=#{bar}"
irb(main):003:1> end
=> nil

现在我想检查它是否已经定义，

Now I'd like to check if it has been defined,

irb(main):004:0> defined?(foo=)
SyntaxError: compile error
(irb):4: syntax error, unexpected ')'
 from (irb):4
 from :0

这里使用的正确语法是什么?我认为必须有一种方法可以转义 "foo=" 以便它被解析并正确传递给定义的?操作员.

What is the proper syntax to use here? I assume there must be a way to escape "foo=" such that it is parsed and passed correctly to the defined? operator.

推荐答案

问题在于 foo= 方法旨在用于分配.您可以通过以下方式使用 defined? 来查看发生了什么:

The problem is that the foo= method is designed to be used in assignments. You can use defined? in the following way to see what's going on:

defined?(self.foo=())
#=> nil
defined?(self.foo = "bar")
#=> nil

def foo=(bar)
end

defined?(self.foo=())
#=> "assignment"
defined?(self.foo = "bar")
#=> "assignment"

比较:

def foo
end

defined?(foo)
#=> "method"

要测试是否定义了 foo= 方法，您应该使用 respond_to? 代替:

To test if the foo= method is defined, you should use respond_to? instead:

respond_to?(:foo=)
#=> false

def foo=(bar)
end

respond_to?(:foo=)
#=> true

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