Ruby支持像PHP这样的var引用吗？

Question

In PHP, you can make two variables point to the same data.

$a = 'foo';
$b = 'bar';
$a =& $b;
echo $a // Outputs: bar
echo $b // Outputs: bar

What we are trying to do in Ruby is set @app_session to be equal to session[@current_app[:uid]] . So we only have to deal with @app_session in our app, and everything is automatically saved to the session.

Is there a way to do this in Ruby? After 15 minutes of reading, googling, and asking around here at the office, we're still lost... lol

Answer 1

All variables in Ruby are references to an object.

a = b

means that a and b point to the same object. That's why when you want to copy a given object, you need to write

a = b.dup

Writing

@app_session = session[@current_app[:uid]]

points to the same object so you should be fine.

EDIT: you can verify this this way:

irb(main):001:0> a = 1
=> 1
irb(main):002:0> b = a
=> 1
irb(main):004:0> p a.object_id
3
=> nil
irb(main):005:0> p b.object_id
3

Answer 2

Variables and constants are pointers to memory locations. Ruby does this by defaut, so you don't have to "emulate" the PVP behaviour by hand. Evidence:

a = "hi"
b = a
a.upcase!
puts a
# => "HI"
puts b
# => "HI"

As for your @app_session question, I'd do something like this:

class ApplicationController < ActionController::Base
  def app_session
    session[@current_app[:uid]]
  end
end

This lets you call the method 'app_session', so that you can easily change the implementation later on. (Say, if you find out that you need to use a constant instead of an instance variable, or whatever.)

Answer 3

Agree with leethal and Keltia. Just one thing to point out:

When you assign some string to a variable, you ALWAYS create a new String object, by doing so.

a = "foo"  # Create a new String object and make a refer this object.
b = "bar"  # Create a new String object and make b refer this object.
a = b      # Make b refer the object created in the first step.
a = "blah" # Create a new String object and make a refer this object. (!)
puts b     # But(!) b is still "foo", because it still refers the "foo" object.
# => "foo"

Answer 4

Isn't this the default for all ruby objects? It wouldn't make sense to copy an object every time.