ruby : nil?, empty? and blank?的选择

        article = nil
article.nil?  # => true

    

empty? checks if an element - like a string or an array f.e. - is empty:

        # Array
[].empty?   #=> true
# String
"".empty?   #=> true

    

Rails adds the method blank? to the Object class:

An object is blank if it‘s false, empty, or a whitespace string. For example, "", " ", nil, [], and {} are blank.

This simplifies

        if !address.nil? && !address.empty?

    

to

        if !address.blank?

.nil?
- It is Ruby method
- It can be used on any object and is true if the object is nil.
- "Only the object nil responds true to nil?" - RailsAPI
nil.nil? = true
anthing_else.nil? = false
a = nil
a.nil? = true
“”.nil = false
.empty?
- It is Ruby method
- can be used on strings, arrays and hashes and returns true if:

    

• String length == 0
• Array length == 0
• Hash length == 0

        
            
                
                    - Running .empty? on something that is nil will throw a NoMethodError
"".empty = true
" ".empty? = false

.blank?
- It is Rails method
- operate on any object as well as work like .empty? on strings, arrays and hashes.
nil.blank? = true 
[].blank? = true 
{}.blank? = true 
"".blank? = true 
5.blank? == false
- It also evaluates true on strings which are non-empty but contain only whitespace:
"  ".blank? == true"  ".empty? == false
Quick tip: !obj.blank? == obj.present?
activesupport/lib/active_support/core_ext/object/blank.rb, line 17 # (Ruby 1.9) 
def present? 
 !blank?
end
                
            
            

        
    

原文：http://www.cnblogs.com/Fooo/p/4276785.html