# Case not calling class' '===' method? **URL:** \ **Category:** ruby-talk\ **Created:** [27 March 2003 04:11 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368 "2003-03-27T04:11:24Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Ptkwt1](https://avatars.discourse-cdn.com/v4/letter/p/85e7bf/32.png) [@Ptkwt1](https://rubytalk.org/u/Ptkwt1)\ **Post date:** [27 March 2003 04:11 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/1 "2003-03-27T04:11:24Z")
maybe I’m missing something obvious… I’ve defined a ‘===’ operator for my class, but it doesn’t seem to get called by case. Here’s the code: class StateType attr\_accessor :state def initialize(\*states) @states = states @state = states[0] end def ===(state) puts “StateType::===” @state == state end def assign(state) raise “Not a valid state: #{state}” unless @states.include? state @state = state end def \<\<(state) assign(state) end end def what(s) case s when :start "START" when :wash "WASH" when :rinse "RINSE" when :spin "SPIN" when :stop "STOP" else "DUNNO" end end #this returns true: fsmt === :start #=\> prints “StateType::===” what(fsmt) #=\> returns “DUNNO” (and “StateType::===” is not printed) What gives? Phil ---
**Author:** ![Tim\_Bates](https://avatars.discourse-cdn.com/v4/letter/t/3da27b/32.png) [@Tim\_Bates](https://rubytalk.org/u/Tim_Bates)\ **Post date:** [27 March 2003 04:22 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/2 "2003-03-27T04:22:54Z")
Case uses the === operator the opposite way around to what you might expect. irb(main):001:0\> “myString” === /my/ false irb(main):002:0\> /my/ === “myString” 0 irb(main):003:0\> case “myString” irb(main):004:1\> when /my/ irb(main):005:1\> true irb(main):006:1\> end true irb(main):007:0\> case /my/ irb(main):008:1\> when “myString” irb(main):009:1\> true irb(main):010:1\> end nil In the example of case “myString” when /my/ true end Ruby actually calls Regexp#===, not String#=== Tim Bates > **···** > > On Thu, 27 Mar 2003 2:41 pm, Phil Tomson wrote: > > > maybe I’m missing something obvious… > > – > tim@bates.id.au ---
**Author:** ![Yukihiro\_Matsumoto2](https://avatars.discourse-cdn.com/v4/letter/y/b9e5f3/32.png) [@Yukihiro\_Matsumoto2](https://rubytalk.org/u/Yukihiro_Matsumoto2)\ **Post date:** [27 March 2003 04:32 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/3 "2003-03-27T04:32:14Z")
Hi, > maybe I’m missing something obvious… > > I’ve defined a ‘===’ operator for my class, but it doesn’t seem to get > called by case. Here’s the code: In a code like case a when b … end “===” is called like “b === a”, not “a === b”. I hope this explains what happened on your code. ``` matz. ``` > **···** > > In message “case not calling class’ ‘===’ method?” on 03/03/27, Phil Tomson [ptkwt@shell1.aracnet.com](mailto:ptkwt@shell1.aracnet.com) writes: ---
**Author:** ![Ptkwt1](https://avatars.discourse-cdn.com/v4/letter/p/85e7bf/32.png) [@Ptkwt1](https://rubytalk.org/u/Ptkwt1)\ **Post date:** [27 March 2003 05:31 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/4 "2003-03-27T05:31:34Z")
In article [1048739230.024452.29873.nullmailer@picachu.netlab.jp](mailto:1048739230.024452.29873.nullmailer@picachu.netlab.jp), > **···** > > Yukihiro Matsumoto [matz@ruby-lang.org](mailto:matz@ruby-lang.org) wrote: > > > Hi, > > > > In message “case not calling class’ ‘===’ method?” \> on 03/03/27, Phil Tomson [ptkwt@shell1.aracnet.com](mailto:ptkwt@shell1.aracnet.com) writes: > > > > > maybe I’m missing something obvious… > > > > > > I’ve defined a ‘===’ operator for my class, but it doesn’t seem to get > > > called by case. Here’s the code: > > > > In a code like > > > > case a > > when b > > … > > end > > > > “===” is called like “b === a”, not “a === b”. I hope this explains > > what happened on your code. > > > > ``` > > matz. > > > > ``` > > Thanks matz. Could you explain why it is done this way? > > Phil ---
**Author:** ![Chris18](https://avatars.discourse-cdn.com/v4/letter/c/e8c25b/32.png) [@Chris18](https://rubytalk.org/u/Chris18)\ **Post date:** [27 March 2003 06:37 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/5 "2003-03-27T06:37:40Z")
Thanks matz. Could you explain why it is done this way? > **···** > > ----- Original Message ----- > From: “Phil Tomson” [ptkwt@shell1.aracnet.com](mailto:ptkwt@shell1.aracnet.com) > > * * * > > Well, I’m not Matz, but I’ll give it a shot… > > It works this way because this is how you want it. 🙂 > > In a case statement, you are trying to fit an object into one of many > different categories. You could try to have every object figure out what > categories it belongs to (terribly difficult), or you could have each > category figure out what belongs in it (easy). > > Just look at some examples of case statements: > > x = 5 > > case x > when 4 then … > when 5 then … > … > end > > case x > when String then … > when Fixnum then … > … > end > > case x > when 0…3 then … > when 3…6 then … > … > end > > Imagine trying to code Fixnum#=== with this in mind: > > class Fixnum > def === other > if other.kind\_of? Fixnum > self == other > elsif other.kind\_of? Module > self.kind\_of? other > elsif other.kind\_of? Range > … > … > end > end > end > > You’d almost have to use a case statement! Seem like a bad idea yet? If > not, imagine the code in String#=== or Array#===; most of it would be > identical to what is in Fixnum#===. > > The current system is definitely the Right Way. > > Chris ---
**Author:** ![Ptkwt1](https://avatars.discourse-cdn.com/v4/letter/p/85e7bf/32.png) [@Ptkwt1](https://rubytalk.org/u/Ptkwt1)\ **Post date:** [27 March 2003 19:14 UTC](https://rubytalk.org/t/case-not-calling-class-method/5368/6 "2003-03-27T19:14:43Z")
In article [060c01c2f42b$9fa30fb0$6401a8c0@MELONBALLER](mailto:060c01c2f42b$9fa30fb0$6401a8c0@MELONBALLER), > **···** > > Chris Pine [nemo@hellotree.com](mailto:nemo@hellotree.com) wrote: > > > ----- Original Message ----- > > From: “Phil Tomson” [ptkwt@shell1.aracnet.com](mailto:ptkwt@shell1.aracnet.com) > > > > ## Thanks matz. Could you explain why it is done this way? > > > > Well, I’m not Matz, but I’ll give it a shot… > > > > It works this way because this is how you want it. 🙂 > > > > In a case statement, you are trying to fit an object into one of many > > different categories. You could try to have every object figure out what > > categories it belongs to (terribly difficult), or you could have each > > category figure out what belongs in it (easy). > > > > Just look at some examples of case statements: > > > > x = 5 > > > > case x > > when 4 then … > > when 5 then … > > … > > end > > > > case x > > when String then … > > when Fixnum then … > > … > > end > > > > case x > > when 0…3 then … > > when 3…6 then … > > … > > end > > > > Imagine trying to code Fixnum#=== with this in mind: > > > > class Fixnum > > def === other > > if other.kind\_of? Fixnum > > self == other > > elsif other.kind\_of? Module > > self.kind\_of? other > > elsif other.kind\_of? Range > > … > > … > > end > > end > > end > > > > You’d almost have to use a case statement! Seem like a bad idea yet? If > > not, imagine the code in String#=== or Array#===; most of it would be > > identical to what is in Fixnum#===. > > > > The current system is definitely the Right Way. > > > > Chris > > Makes sense… Thanks for the explanation. > > Phil