What is the point of using “send” instead of a nor

问题:

as far as I understand 'send' method, this

some_object.some_method("im an argument")

is same as this

some_object.send :some_method, "im an argument"

So what is the point using 'send' method?

回答1:

It can come in handy if you don't know in advance the name of the method, when you're doing metaprogramming for example, you can have the name of the method in a variable and pass it to the send method.

It can also be used to call private methods, although this particular usage is not considered to be a good practice by most Ruby developers.

class Test
  private
  def my_private_method
    puts "Yay"
  end
end

t = Test.new

t.my_private_method # Error

t.send :my_private_method #Ok

You can use public_send though to only be able to call public methods.

回答2:

In addition to Intrepidd's use cases, it is convenient when you want to route different methods on the same receiver and/or arguments. If you have some_object, and want to do different things on it depending on what foo is, then without send, you need to write like:

case foo
when blah_blah then some_object.do_this(*some_arguments)
when whatever then some_object.do_that(*some_arguments)
...
end

but if you have send, you can write

next_method =
case foo
when blah_blah then :do_this
when whatever then :do_that
....
end
some_object.send(next_method, *some_arguments)

or

some_object.send(
  case foo
  when blah_blah then :do_this
  when whatever then :do_that
  ....
  end,
  *some_arguments
)

or by using a hash, even this:

NextMethod = {blah_blah: :do_this, whatever: :do_that, ...}
some_object.send(NextMethod[:foo], *some_arguments)

回答3:

In addition to everyone else's answers, a good use case would be for iterating through methods that contain an incrementing digit.

class Something
  def attribute_0
    "foo"
  end
  def attribute_1
    "bar"
  end
  def attribute_2
    "baz"
  end
end

thing = Something.new

3.times do |x|
  puts thing.send("attribute_#{x}")
end

#=> foo
# bar
# baz

This may seem trivial, but it's occasionally helped me keep my Rails code and templates DRY. It's a very specific case, but I think it's a valid one.

回答4:

The summing briefly up what was already said by colleagues: send method is a syntax sugar for meta-programming. The example below demonstrates the case when native calls to methods are likely impossible:

class Validator
  def name
    'Mozart'
  end
  def location
    'Salzburg'
  end
end

v = Validator.new
'%name% was born in %location%'.gsub (/%(?<mthd>\w+)%/) do
  # v.send :"#{Regexp.last_match[:mthd]}"
  v.send Regexp.last_match[:mthd].to_sym
end
=> "Mozart was born in Salzburg" 

回答5:

I like this costruction

Object.get_const("Foo").send(:bar)