Checking If a Variable Is Not Nil and Not Zero in Ruby

Checking if a variable is not nil and not zero in ruby

unless discount.nil? || discount == 0
  # ...
end

Check if not nil and not empty in Rails shortcut?

There's a method that does this for you:

def show
  @city = @user.city.present?
end

The present? method tests for not-nil plus has content. Empty strings, strings consisting of spaces or tabs, are considered not present.

Since this pattern is so common there's even a shortcut in ActiveRecord:

def show
  @city = @user.city?
end

This is roughly equivalent.

As a note, testing vs nil is almost always redundant. There are only two logically false values in Ruby: nil and false. Unless it's possible for a variable to be literal false, this would be sufficient:

if (variable)
  # ...
end

This is preferable to the usual if (!variable.nil?) or if (variable != nil) stuff that shows up occasionally. Ruby tends to wards a more reductionist type of expression.

One reason you'd want to compare vs. nil is if you have a tri-state variable that can be true, false or nil and you need to distinguish between the last two states.

How to check for nil and compare if != nil on Hashes?

If you want to check if an object/value is nil you can do it like this:

object.nil?

in your case (the value of a hash is something like): your_hash[key].nil?, with that said if you want to do something if the value is not nil you can do:

if !my_hash[my_key].nil?
end

or the ruby way:

unless my_hash[my_key].nil?
end

Also if you want to know whether a hash contains or not a key you can do it as follow:

your_hash.keys.include? key_to_search

If you want to compare 2 strings: str1 == str2, if you want to know if str1 contains to str2 as substring then str1.include? str2

Best ruby idiom for nil or zero

Objects have a nil? method.

if val.nil? || val == 0
  [do something]
end

Or, for just one instruction:

[do something] if val.nil? || val == 0

Is there a Ruby, or Ruby-ism for not_nil? opposite of nil? method?

when you're using ActiveSupport, there's user.present? http://api.rubyonrails.org/classes/Object.html#method-i-present%3F, to check just for non-nil, why not use

def logged_in?
  user # or !!user if you really want boolean's
end

Checking if variable is nil or empty in a single line using or operator

It's a matter of operator precedence. || has a higher precedence than or.
You should write it like:

str = nil
puts (str.nil? or str.empty?)
puts str.nil? || str.empty?

See more in Difference between "or" and || in Ruby?

For the issue of FPM, I have tried under Ruby 1.8.6, 1.9.3, 2.0.0, and did not get error with or expression.

Ruby way to check if a string is not blank?

string = ""

unless string.to_s.strip.empty?
  # ...
end

Checking if an answer is empty or not

use below code:

puts "Enter your age."
age = Integer(gets.chomp) rescue nil
while age.nil?
 age = Integer(gets.chomp) rescue nil
end

How to idiomatically check if a Hash is not nil and so get value of a key in one line in Ruby on Rails?

A typical way would be val = hash && hash[key] or val = hash[key] if hash.

You can also use the safe navigation operator, like val = hash&.dig(key) (see Hash#dig) or val = hash&.[](key) .. I wouldn't really recommend that last one since it's not very readable

All of those examples will set val to nil if the hash is nil. If the key must exist and you want to raise an error if it doesn't, you can use val = hash&.fetch(key) (see Hash#fetch)

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