如何判断某个方法是否已在类中定义? [英] How to judge whether a method has defined in a class?
问题描述
class C1
unless method_defined? :hello # Certainly, it's not correct. I am asking to find something to do this work.
def_method(:hello) do
puts 'Hi Everyone'
end
end
end
那么,如何判断方法是否已定义?
So, how to judge whether a method has defined or not?
推荐答案
您发布的代码可以很好地检查方法是否已定义. Module#method_defined?
确实是正确的选择. (还有变体 Module#public_method_defined?
, Module#protected_method_defined?
和 Module#define_method
).
The code you posted works just fine for checking whether the method is defined or not. Module#method_defined?
is exactly the right choice. (There's also the variants Module#public_method_defined?
, Module#protected_method_defined?
and Module#private_method_defined?
.) The problem is with your call to def_method
, which doesn't exist. (It's called Module#define_method
).
这就像一种魅力:
class C1
define_method(:hello) do
puts 'Hi Everyone'
end unless method_defined? :hello
end
但是,由于您已经预先知道名称并且不使用任何闭包,因此无需使用Module#define_method
,您可以只使用def
关键字:
However, since you already know the name in advance and don't use any closure, there is no need to use Module#define_method
, you can just use the def
keyword instead:
class C1
def hello
puts 'Hi Everyone'
end unless method_defined? :hello
end
还是我误解了您的问题,而您担心继承?在这种情况下,Module#method_defined?
不是正确的选择,因为它遍历了整个继承链.在这种情况下,您将必须使用 Module#instance_methods
或它的一个堂兄 Module#public_instance_methods
, Module#private_instance_methods
,它带有一个可选参数,告诉他们是否包括超类/混合类中的方法. (请注意,该文档是错误的:如果不传递任何参数,它将将包含所有继承的方法.)
Or have I misunderstood your question and you are worried about inheritance? In that case, Module#method_defined?
is not the right choice, because it walks the entire inheritance chain. In that case, you will have to use Module#instance_methods
or one of its cousins Module#public_instance_methods
, Module#protected_instance_methods
or Module#private_instance_methods
, which take an optional argument telling them whether to include methods from superclasses / mixins or not. (Note that the documentation is wrong: if you pass no arguments, it will include all the inherited methods.)
class C1
unless instance_methods(false).include? :hello
def hello
puts 'Hi Everyone'
end
end
end
这里有一个小测试套件,表明我的建议有效:
Here's a little test suite that shows that my suggestion works:
require 'test/unit'
class TestDefineMethodConditionally < Test::Unit::TestCase
def setup
@c1 = Class.new do
def self.add_hello(who)
define_method(:hello) do
who
end unless method_defined? :hello
end
end
@o = @c1.new
end
def test_that_the_method_doesnt_exist_when_it_hasnt_been_defined_yet
assert !@c1.method_defined?(:hello)
assert !@c1.instance_methods.include?(:hello)
assert !@o.methods.include?(:hello)
assert !@o.respond_to?(:hello)
assert_raise(NoMethodError) { @o.hello }
end
def test_that_the_method_does_exist_after_it_has_been_defined
@c1.add_hello 'one'
assert @c1.method_defined?(:hello)
assert @c1.instance_methods.include?(:hello)
assert @o.methods.include?(:hello)
assert_respond_to @o, :hello
assert_nothing_raised { @o.hello }
assert_equal 'one', @o.hello
end
def test_that_the_method_cannot_be_redefined
@c1.add_hello 'one'
assert @c1.method_defined?(:hello)
assert @c1.instance_methods.include?(:hello)
assert @o.methods.include?(:hello)
assert_respond_to @o, :hello
assert_nothing_raised { @o.hello }
assert_equal 'one', @o.hello
@c1.add_hello 'two'
assert @c1.method_defined?(:hello)
assert @c1.instance_methods.include?(:hello)
assert @o.methods.include?(:hello)
assert_respond_to @o, :hello
assert_nothing_raised { @o.hello }
assert_equal 'one', @o.hello, 'it should *still* respond with "one"!'
end
end
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