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
So, how to judge whether a method has defined or not?
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
).
This works like a charm:
class C1
define_method(:hello) do
puts 'Hi Everyone'
end unless method_defined? :hello
end
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
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
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 [email protected]_defined?(:hello)
assert [email protected]_methods.include?(:hello)
assert [email protected]?(:hello)
assert [email protected]_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
Look at the Ruby Object class. It has a methods
function to get an list of methods and a respond_to?
to check for a specific method. So you want code like this:
class C1
def add_hello
unless self.respond_to? "hello"
def hello
puts 'Hi Everyone'
end
end
end
end
cone.hello #This would fail
cone.add_hello
cone.hello #This would work
The Object class has the method "methods": docs
class Klass
def kMethod()
end
end
k = Klass.new
k.methods[0..9] #=> ["kMethod", "freeze", "nil?", "is_a?",
# "class", "instance_variable_set",
# "methods", "extend", "__send__", "instance_eval"]
k.methods.length #=> 42
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