Ruby里4种比较函数（equal?, eql?, ==, ===）详解

(编辑：jimmy 日期: 2024/10/4 浏览：2)

Ruby里面有4种比较方法，equal"htmlcode"> 

 a = "abc"
#=> "abc"

 b = a + ""
#=> "abc"

?> a == b
#=> true

 a.object_id
#=> 70255156346640

 b.object_id
#=> 70255156340640

=== - 用在 case 语句里时会调用的方法

通常用在 case 比较调用该方法，比如

case some_object
when /a regex/
 # The regex matches
when String
 # some_object is kind of String
when 2..4
 # some_object is in the range 2..4
when lambda {|x| some_crazy_custom_predicate }
 # the lambda returned true
end

等同于

if /a regex/ === some_object
 # The regex matches
elsif String === some_object
 # some_object is kind of object
elsif (2..4) === some_object
 # some_object is in the range 2..4
elsif lambda {|x| some_crazy_custom_predicate } === some_object
 # the lambda returned true
end

eql"htmlcode"> 

1 == 1.0  #=> true
1.eql"htmlcode">



[1] pry(main)> hash = Hash.new
#=> {}
[2] pry(main)> hash[2] = "a"
#=> "a"
[3] pry(main)> hash[2.0] = "b"
#=> "b"
[4] pry(main)> hash[2]
#=> "a"
[5] pry(main)> hash[2.0]
#=> "b"
[6] pry(main)> hash[2.00] = "c"
#=> "c"
[7] pry(main)> hash[2.0]
#=> "c"






所以什么时候应该覆盖这个方法就看你想让他在 Hash 比较时如何表现。


equal"htmlcode">



q = User.first
 User Load (40.4ms) SELECT "users".* FROM "users"  ORDER BY "users"."id" ASC LIMIT 1
#=> #<User id: 1, email: "ryan@wongyouth.com">

q2 = User.first
 User Load (0.4ms) SELECT "users".* FROM "users"  ORDER BY "users"."id" ASC LIMIT 1
#=> #<User id: 1, email: "ryan@wongyouth.com">

q.equal? q2
#=> false







记忆方法


    
  
  1. == 按业务需求覆盖该方法
    2. 
  
  2. === 覆盖 case 语句时的表现
    3. 
  
  3. eql? 别名到 == 方法, 需要时覆盖方法改变 Hash 比较时的表现
    4. 
  
  4. equal? 不改动
    5.
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