Couldnt understand the Array behavior in ruby

Question

i was writing code to append new email to an empty array in my Rails App. like this:

@users_email = Array.new 
@users_email << User.find_by_id(@comment.user_id).email 
@users_email << User.find_by_id(Comment.find_by_id(@parent_id).user_id).email if !@parent_id.nil?

Note: Here @comment is just a hash of id, user_id, parent_id and @parent_id is a the id of a Parent of any Comment. as in Hierarchy of Parent-child.

But instead of having two items in array ex: ["[email protected]", "[email protected]"] I am getting only one item ex:["[email protected]"] after appending second item.

My confusion starts when I try to save above expression in an Instance variable and tries to append the same into an empty array, It behaves as expected. Ex:

@users_email = Array.new
@first = User.find_by_id(@comment.user_id).email
@second = User.find_by_id(Comment.find_by_id(@parent_id).user_id).email if !@parent_id.nil?

@users_email << @first  # ["[email protected]"]
@users_email << @second  # ["[email protected]", "[email protected]"]

where as this wasn't the case in previous one. Can someone please explain whats happening here.

Update

By mistake I have place "=" instead of "<<" while appending first element to the array for the first case and after appending second one I got the result something like "[email protected]@xyz.com" but for some reason in my Rails Application I was getting only the first email id in return.ex: ["[email protected]"]

So, probably this question is now not relevant to the issue raised. Sorry for bugging all of you.

In your last code block you've got @user_email = Array.new, @users_email << @first and @user_email << @second. Was that a typo in the @users_email << @first part? (there's an s in there, which isn't on the other two lines). Also, in Ruby you usually write [] over Array.new. So, instead of @user_email = Array.new you would have @user_email = []. — Kevin
– Kevin, Commented May 24, 2015 at 6:14
Ok, so was the content of @comment.user_id the same in both cases? — Kevin
– Kevin, Commented May 24, 2015 at 6:24
Yes its the same in both case..infact both the use case are having exact input just the change in writing code — Abhinay
– Abhinay, Commented May 24, 2015 at 6:26
are you sure you got ["[email protected]"] instead of ["[email protected]"] when you were expecting ["[email protected]", "[email protected]"]? — Shiva
– Shiva, Commented May 24, 2015 at 7:12

fny · Accepted Answer · 2015-05-24 06:13:23Z

1

That's because you have this check !@parent_id.nil? at the end of the following statement:

 @users_email << User.find_by_id(Comment.find_by_id(@parent_id).user_id).email if !@parent_id.nil?

In the first case, @parent_id apparently is nil, so the statement never executes: hence only one value is appended to the array.

Aside: prefer using the array literal syntax (ary = [] over ary = Array.new)

answered May 24, 2015 at 6:13

fny

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6 Comments

Kevin Over a year ago

That line is also in his second code block. There are some typos in that code block though (as I mentioned in my comment on his post).

fny Over a year ago

I realize that, but, like I said, in the first case, @parent_id must have been nil while in the second case it wasn't. I'm fairly certain the behavior you're seeing is just a coincidence since the behavior of the two blocks is nearly identical aside from the additional instance variables.

Kevin Over a year ago

Yeah, I understand that, but he got ["[email protected]"] in his first try. That's from that second line, the line that you mentioned in your answer.

Abhinay Over a year ago

Also, using [] over Array.new doesn't affect the behavior if i am not wrong

fny Over a year ago

No it doesn't. It's just poor style. Regarding your code, it must have been nil or @second had to have been defined before. It's impossible for the return of that line (User.find_by ... if !@parent_id.nil?) to differ otherwise.

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