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Rails: nil?, empty?, blank?, present?の挙動

Last updated at Posted at 2014-09-12

Rails開発でnil?, empty?, blank?, present?の挙動にハマったのでメモ

以下の値で書くメソッドについて比較してみる。

var.rb
a = nil
b = true
c = false
d = []
e = [123]
f = 123

nil?

nil.rb
a.nil? #=> true
b.nil? #=> false
c.nil? #=> false
d.nil? #=> false
e.nil? #=> false 

empty?

empty.rb
a.empty? #=> undefined method `empty?' for nil:NilClass
b.empty? #=> undefined method `empty?' for true:TrueClass
c.empty? #=> undefined method `empty?' for false:FalseClass
d.empty? #=> true
e.empty? #=> false
f.empty? #=> undefined method `empty?' for 123:Fixnum

blank?

blank.rb
a.blank? #=> true
b.blank? #=> false
c.blank? #=> true
d.blank? #=> true
e.blank? #=> false
f.blank? #=> false

present?

present.rb
a.present? #=> false
b.present? #=> true
c.present? #=> false
d.present? #=> false
e.present? #=> true
f.present? #=> true

Rubyの条件式を用いた場合

if.rb
puts a ? true : false #=> false
puts b ? true : false #=> true
puts c ? true : false #=> false
puts d ? true : false #=> true
puts e ? true : false #=> true
puts f ? true : false #=> true

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