.nil?

nil.nil?       #true
[].nil?        #false
{}.nil?        #false
"".nil?        #false
" ".nil?       #false
"abc".nil?     #false
123.nil?       #false

• ruby method
• 任何物件都是 false，只有 nil 是 true

.empty? & .any?

nil.empty?     #NoMethodError: undefined method `empty?' for nil:NilClass
[].empty?      #true
{}.empty?      #true
"".empty?      #true
" ".empty?     #false
"abc".empty?   #false
123.empty?     #NoMethodError: undefined method `empty?' for 123:Fixnum

• ruby method
• 只要是空值就是 true（空白不算空值）
• 相對的 method 是 any?

nil.any?       #NoMethodError: undefined method `any?' for nil:NilClass
[].any?        #false
{}.any?        #false
"".any?        #NoMethodError: undefined method `any?' for "":String
" ".any?       #NoMethodError: undefined method `any?' for "":String
"abc".any?     #NoMethodError: undefined method `any?' for "":String
123.any?       #NoMethodError: undefined method `any?' for 123:Fixnum

• 但是要注意，String 並沒有提供 .any? 這個 method

.blank? & .present?

nil.blank?     #true
[].blank?      #true
{}.blank?      #true
"".blank?      #true
" ".blank?     #true
"abc".blank?   #false
123.blank?     #false

• Rails method
• 只要是 nil，空值都是 true
• 有點像是 Object.nil? || Object.empty? 的綜合體，但條件比 .empty 寬鬆一點，空白也會是 true
• 相對的 method 是 present?

nil.present?   #false
[].present?    #false
{}.present?    #false
"".present?    #false
" ".present?   #false
"abc".present? #true
123.present?   #true