<% if dashboard_pane_counter.remainder(3) == 0 %>
do something
<% end>
If dasboard_pane_counter wasn't defined, how can I get this to evaluate to false rather than throw an exception?
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6 Answers
<% if defined?(:dashboard_pane_counter) && dashboard_pane_counter.remainder(3) == 0 %>
# do_something here, this assumes that dashboard_pane_counter is defined, but not nil
<% end %>
1 Comment
HungryCoder
symbol did not work for me. so i had to check this way
if defined?(variable_name)When using rails and instance variables, nil has a try method defined, so you can do:
<% if @dashboard_pane_counter.try(:remainder(3)) == 0 %>
#do something
<% end %>
so if the instance variable is not defined, try(:anything) will return nil and therefore evaluate to false. And nil == 0 is false
4 Comments
michaeltwofish
This will still cause an error if the variable hasn't been defined, so doesn't answer the question.
Yule
No it won't, rails has 'magic built in':
1.9.3p392 :005 > @hh => nil 1.9.3p392 :006 > @hh.try(:anything) => nil Yule
So for instance variables, nil has a 'try' method
michaeltwofish
Ah, you're right, my mistake. If you edit your answer to that clear I can remove my down vote.
local_assigns can be used for that, since this question is from a few years ago, I verified that it exists in previous versions of rails
<% if local_assigns[:dashboard_pane_counter]
&& dashboard_pane_counter.remainder(3) == 0%>
<% end %>
It's in the notes here
Comments
Posting this answer for beginner coders like myself. This question can be answered simply using two steps (or one if using &&). It is a longer and less pretty answer but helps new coders to understand what they are doing and uses a very simple technique that is not present in any of the other answers yet. The trick is to use an instance (@) variable, it will not work with a local variable:
if @foo
"bar"
end
If @foo is defined it will be return "bar", otherwise not (with no error). Therefore in two steps:
if @dashboard_pane_counter
if @dashboard_plane_counter.remainder(3) == 0
do something
end
end
Comments
Another way, with a neat gem, is 'andand.'
Comments
Insted of
if !var.nil?
I would use
unless var.nil?
Thats much better ruby code!
1 Comment
baash05
this only applies if the variable was defined previous to this code. Try if !adallajglaksdkfaj.nil? on the first line of a "function". kablammo :)