I always meet this Ruby problem, I want to write it more cleanly.
var a can be nil
a.value can also be nil
a.value has possible true or false value
if (not a.nil?) && (not a.value.nil?) && a.value == false
puts "a value is not available"
else
puts "a value is true"
end
The problem is that the conditional statement is too clumsy and hard to read.
How can I improve the checking nil and false conditional statement?
Thanks, I am a Ruby newbie
Ruby on rails has an extension called try which allows you to write:
if a.try(:value) == false
which is very clean. Without try, you can just write
if a && a.value == false
If a.value is nil, it is not false, so that is ok :)
If it is possible that a.value is not defined (which would raise an exception), I would write that as follows:
if a && a.respond_to?(:value) && a.value == false
[UPDATE: after ruby 2.3]
Since ruby 2.3 there is an even shorter version:
if a&.value == false
which is almost equivalent to a.try(:value) (but is pure ruby). Differences:
value does not exist, the &. operator will throw, try will just return nil (preferable or not?)(note: try! would also throw). try or &. they also handle false differently. This follows logically from previous difference, try will return nil, while &. will throw because false knows no methods :P 
false.value, and that has the possibility of being false, then the result would be different. But I assumed that may not be the case and gave +1 here.
a.value ||= true --> which will always set it to true, because false and nil will return false. But in this case it is just fine.
a value that's either nil or defined with a value property exposed, you're not responsible for handling oddball cases where value is not present. Let it blow up. The caller's responsible for making the correct call.You can achieve it in more compacted way using Safe Navigation Operator (&.):
if a&.value == false
Source : http://mitrev.net/ruby/2015/11/13/the-operator-in-ruby/
if a && a.value!=false
puts "a value is true"
else
puts "a value is not available"
end
or just
puts a && a.value!=false ? "a value is true" : "a value is not available"
puts a && a.value ? "a value is true" : "a value is not available" cause in ruby nil and false in an argument considered as falseblank?. Also, this is not equivalent to the OP's code. This code puts "a value is not available" when a.value is nil, but the OP's code puts "a value is true".The simplest and cleanest way is to flip it and reverse it. Check for the truthy value rather than the falsey values
if a && a.value
puts "a value is true"
else
puts "a value is not available"
end
Of course in Rails you could do it either way by using blank? or present?
Your condition is redundant. If a.value is to be false, then it would not be nil.
if a.nil?.! && a.value == false
puts "a value is not available"
else
puts "a value is true"
end
false, it cannot be nil.
Boolean#!.
! operator translate into a message send as opposed to being bultin was introduced in Ruby 1.9.0.This will always return a boolean, if nil it will return false; if false it returns false; if true returns true. Try it out, it's nice and short:
!!a.try(:value) == false
a.valuebeingnilwould raise an error, then why do you put that in the condition? It does not make sense because the error would be raised anyway.ais nil, not ifa.valueis nil.ais a class andvalueis not defined.