empty?とblank?とnil?

Rails Ruby

環境

ruby 1.9.3p194
Rails 3.2.3

空文字列

"".empty? # true
"".blank?  # true
"".nil?       # false

空配列

[].empty? # true
[].blank?  # true
[].nil?       # false

空ハッシュ

{}.empty? # true
{}.blank?  # true
{}.nil?       # false

空Proc

Proc.new{}.empty? # NoMethodError: undefined method `empty?'
Proc.new{}.blank?  # false
Proc.new{}.nil?       # false

lambda{}.empty?    # NoMethodError: undefined method `empty?'
lambda{}.blank?     # false
lambda{}.nil?          # false

nil

nil.empty? #NoMethodError: undefined method `empty?'
nil.blank?  #true
nil.nil?       #true

false

false.empty? #NoMethodError: undefined method `empty?'
false.blank?  #true
false.nil?       #false