dynamic variable names using Ruby's instance_variable_set

Question

I'm trying to create a set of instances that have different instance names using instance_variable_set to change the instance name and I can't seem to get it to work.

 for i in 0..3 do
   username_str   = String.new
   username_str   = 'user_' + i.to_s

   username_new   = User.new
   username_new.instance_variable_set("@#{WHAT_DO_I_PUT_HERE?}", username_str)

   username_new = User.create(:username => username_str)

 end

The part I can't figure out is what do I put in the first field of instance_variable_set where I have "WHAT_DO_I_PUT_HERE?"?

This isn't an answer to what you're asking, but it's worth pointing out since it's surely a mistake: You're setting username_new to a User instance, setting an instance variable on that object, then throwing the object away and setting it to a new object that you get from User.create. — Chuck
– Chuck, Commented Oct 21, 2010 at 21:11
@Chuck: What I am trying to do is create a bunch of Users with different usernames. The worry I had was that I didn't think I could reuse the username_new variable each time through the loop. Maybe I am wrong about that, although I've tried removing the line with instance_variable_set, and that doesn't work either. — James Testa
– James Testa, Commented Oct 21, 2010 at 21:21

Wayne Conrad · Accepted Answer · 2010-10-21 22:37:23Z

4

Instance variables might be the wrong tool for the job. If all you want to do is create three users, then:

3.times do |i|
  User.create(:username => "user_#{i}")
end

If you need to retain the User objects for later use, then you can use an array:

@users = 3.times.map do |i|
  User.create(:username => "user_#{i}")
end

after which @users[0] will retrieve the first instance of User, @users[1] the second, &c.

answered Oct 21, 2010 at 22:37

Wayne Conrad

109k26 gold badges158 silver badges195 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

James Testa Over a year ago

Yup, this is all I needed. I actually had this, but because there was a bug in the parameters I was using for User.create(params), the users weren't getting created. So I came across instance_variable_set, thinking that would fix the problem, when in reality there was just a bug in my code :-) Thanks again!

Wayne Conrad Over a year ago

@james Testa, You're welcome! By the way, if you use create! instead of create, you'll get a nice exception if it doesn't get created.

Chuck · Accepted Answer · 2010-10-21 19:11:43Z

0

You would put a string containing the name of the instance variable you want to set. Alternatively, if you do not have such a string, you could just skip the string interpolation and write the name of the instance variable in there yourself.

answered Oct 21, 2010 at 19:11

Chuck

238k31 gold badges306 silver badges392 bronze badges

3 Comments

James Testa Over a year ago

Wouldn't the string with the name of the instance variable I want to set be "username_new"? I tried putting "username_new" there and I got an error.

Chuck Over a year ago

@James Testa: No, the variable username_new references an instance of User, not a String. The error you got was probably along the lines of "This is not a valid name for an instance variable." Whatever instance variable in User represents the name is what you'd want to use there.

James Testa Over a year ago

Boy, I'm still confused. What I am trying to do is create a bunch of users with different user names using a for loop. Is username_new an instance variable? Or in this case would "username" be an instance variable?

Collectives™ on Stack Overflow

dynamic variable names using Ruby's instance_variable_set

2 Answers 2

2 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related