Ruby里4种比较函数（equal?, eql?, ==, ===）详解

(编辑：jimmy 日期: 2024/11/16 浏览：3 次 )

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

== 按业务需求覆盖该方法

=== 覆盖 case 语句时的表现

eql? 别名到 == 方法, 需要时覆盖方法改变 Hash 比较时的表现

equal? 不改动

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