# How the Ruby's super work in finding method?

**URL:** <https://www.ruby-forum.com/t/how-the-rubys-super-work-in-finding-method/153683>\
**Category:** Ruby\
**Created:** [November 20, 2008, 4:27am UTC](https://www.ruby-forum.com/t/how-the-rubys-super-work-in-finding-method/153683 "2008-11-20T04:27:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![qianjigui](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/q/9e8a1a/32.png) [@qianjigui](https://www.ruby-forum.com/u/qianjigui)\
**Post date:** [November 20, 2008, 4:27am UTC](https://www.ruby-forum.com/t/how-the-rubys-super-work-in-finding-method/153683/1 "2008-11-20T04:27:34Z")

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When one method defined in many places, I want to use the super to  
invoke them one by one. This is the code:

#########################################  
module M  
def report( a = 4, b =5)  
p “M report begin: a=#{a},b=#{b}”  
a = 6  
super(a)  
p “M report end”  
end  
end

class B  
def report(a=11,b=12)  
p “B report 1 begin: a=#{a},b=#{b}”  
p “B report 1 end”  
end  
def report(a=13,b=14)  
p “B report 2 begin: a=#{a},b=#{b}”  
#super()  
p “B report 2 end”  
end  
end

class C \< B  
def report( a=8,b=9)  
p “C report 1 begin: a=#{a},b=#{b}”  
p “C report 1 end”  
end  
def report( a=7,b=3)  
p “C report 2 begin: a =#{a},b=#{b}”  
super()  
p “C report 2 End”  
end  
include M  
end

class D \< C  
def report( a = 2, b=1)  
p “D report 1 begin: a=#{a},b=#{b}”  
super(a,b)  
p “D report 1 end”  
end  
include M  
def report(a = -2, b=-1)  
p “D report 2 begin: a=#{a},b=#{b}”  
super  
p “D report 2 end”  
end  
end

d = D.new  
d.report

#########################################  
That’s the output:

:!ruby testMethodGet.rb  
“D report 2 begin: a=-2,b=-1”  
“C report 2 begin: a =-2,b=-1”  
“M report begin: a=4,b=5”  
“B report 2 begin: a=6,b=14”  
“B report 2 end”  
“M report end”  
“C report 2 End”  
“D report 2 end”

I find sometimes it will invoke the super class’ method first(D-\>C-\>M),  
but it will invoke the module’s method first(C-\>M-\>B) too.  
I know I include the module in different place in the different classes.  
But I don’t know the strange working .  
Can anyone find the problem?

---

<div class="post-metadata">

**Author:** ![qianjigui](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/q/9e8a1a/32.png) [@qianjigui](https://www.ruby-forum.com/u/qianjigui)\
**Post date:** [November 20, 2008, 4:44am UTC](https://www.ruby-forum.com/t/how-the-rubys-super-work-in-finding-method/153683/2 "2008-11-20T04:44:17Z")

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On Nov 19, 9:23 pm, Qian J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> end  
> p “B report 2 end”  
> super()  
> end
> 
> “C report 2 End”  
> “D report 2 end”
> 
> I find sometimes it will invoke the super class’ method first(D-\>C-\>M),  
> but it will invoke the module’s method first(C-\>M-\>B) too.  
> I know I include the module in different place in the different classes.  
> But I don’t know the strange working .  
> Can anyone find the problem?

First of all, you can’t define a method more than once. That is,  
defining it a second time overwrites any previous definition, so if  
you’re expecting to see B, C, or D report 1, that’s not going to  
happen.

Second, once a module is part of the ancestor chain, re-including it  
doesn’t do anything. You have B by itself, then C inherits from B, so  
the lookup chain is

C → B

Then C includes M

C → M → B

Then D inherits from C

D → C → M → B

Then D includes M, but M is already present as an ancestor

D → C → M → B

---

<div class="post-metadata">

**Author:** ![qianjigui](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/q/9e8a1a/32.png) [@qianjigui](https://www.ruby-forum.com/u/qianjigui)\
**Post date:** [November 20, 2008, 2:40pm UTC](https://www.ruby-forum.com/t/how-the-rubys-super-work-in-finding-method/153683/3 "2008-11-20T14:40:33Z")

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Thanks for your help.  
Now I know more about the module, super, class and the method finding.  
The doesn’t describe detail.

Yossef M. wrote:

> On Nov 19, 9:23�pm, Qian J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:  
> First of all, you can’t define a method more than once. That is,  
> defining it a second time overwrites any previous definition, so if  
> you’re expecting to see B, C, or D report 1, that’s not going to  
> happen.
> 
> Second, once a module is part of the ancestor chain, re-including it  
> doesn’t do anything. You have B by itself, then C inherits from B, so  
> the lookup chain is
> 
> C → B
> 
> Then C includes M
> 
> C → M → B
> 
> Then D inherits from C
> 
> D → C → M → B
> 
> Then D includes M, but M is already present as an ancestor
> 
> D → C → M → B