# Issues with inheritance

**URL:** <https://www.ruby-forum.com/t/issues-with-inheritance/172375>\
**Category:** Ruby\
**Created:** [July 20, 2009, 5:41pm UTC](https://www.ruby-forum.com/t/issues-with-inheritance/172375 "2009-07-20T17:41:39Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Juston\_Davies](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e68b1a/32.png) [@Juston\_Davies](https://www.ruby-forum.com/u/Juston_Davies)\
**Post date:** [July 20, 2009, 5:41pm UTC](https://www.ruby-forum.com/t/issues-with-inheritance/172375/1 "2009-07-20T17:41:39Z")

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I’m building a large system that needs to have a data structure of  
things that look and act similar to one another in a kind of  
composition tree. Take a look at my small scale test code below:

class Main  
def main  
#instantiate objects  
three = Child3.new  
two = Child2.new  
one = Child1.new  
#build tree  
two.addNode three  
one.addNode two  
#execute tree  
one.execute "Who is "  
end  
end

class Parent  
#Has some composing nodes  
@nodes  
#Init code  
def initialize  
@nodes = Array.new  
end  
#add a node to object  
def addNode node  
@nodes \<\< node  
end  
#Generalized execute code  
def execute str  
puts str + self.to\_s  
@nodes.each {|node| node.execute str}  
end  
end

class Child1 \< Parent  
#The same a parent in this scenerio but has other functionality not  
illustrated here  
end

class Child2 \< Parent  
#The same a parent in most cases, needs to do “extra” in execute  
calls  
def execute str  
puts str + self.to\_s  
#@nodes.each {|node| node.execute “Batman?”} \<—This works but its  
really ideal for code recycling  
#str = “Robin” \<—This actually causes subsequent levels to print  
Robin instead of Batman? or Who is  
super.execute “Batman?”  
end  
end

class Child3 \< Parent  
#The same a parent in this scenerio but has other functionality not  
illustrated here  
end  
#Just so I can execute my Test.rb easy in eclipse, not really  
important  
if **FILE** == $0  
Main.new.main  
end

When I designed the code I expected what would print out would be:  
\>Who is   
\>Who is   
\>Batman?   
But I get:  
\>Who is   
\>Who is   
\>Who is   
\>Who is   
\>Error

The first problem I see is that when I call super.execute it seems to  
want to ignore my argument and favor of the argument I gave at the  
hight level of scope. (If I do str = “Robin” in Child2’s execute but  
still call super.execute(“batman”) it prints “\>Robin” in subsequent  
levels.) The second is that Child2 somehow calls execute on itself  
once before digging into the next level of the tree, then at the last  
level it tries to call it on an empty array which goes against the  
program logic. I’m not new to programming, I’ve probably built this  
exact same thing in Java, but I am new to Ruby. Whats wrong with what  
I’m trying to do?

Thanks in advance!

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<div class="post-metadata">

**Author:** ![Juston\_Davies](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e68b1a/32.png) [@Juston\_Davies](https://www.ruby-forum.com/u/Juston_Davies)\
**Post date:** [July 20, 2009, 5:46pm UTC](https://www.ruby-forum.com/t/issues-with-inheritance/172375/2 "2009-07-20T17:46:20Z")

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> The first problem I see is that when I call super.execute it seems to  
> want to ignore my argument and favor of the argument I gave at the  
> hight level of scope. (If I do str = “Robin” in Child2’s execute but  
> still call super.execute(“batman”) it prints “\>Robin” in subsequent  
> levels.) The second is that Child2 somehow calls execute on itself  
> once before digging into the next level of the tree, then at the last  
> level it tries to call it on an empty array which goes against the  
> program logic. I’m not new to programming, I’ve probably built this  
> exact same thing in Java, but I am new to Ruby. Whats wrong with what  
> I’m trying to do?

In Ruby, you just call super() to call the parent method. There are  
three  
use cases for super:

- Implicit args: `super` – this calls the parent method with the same  
arguments as the current method call.
- No args: `super()` – the explicit empty parens mean call the parent  
method with no arguments, whatever the current method was called with.
- Explicit args: `super(arg1, arg2 ...)` – calls the parent method with  
the  
given arguments.

Hope that helps.

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**Author:** ![Juston\_Davies](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e68b1a/32.png) [@Juston\_Davies](https://www.ruby-forum.com/u/Juston_Davies)\
**Post date:** [July 20, 2009, 5:51pm UTC](https://www.ruby-forum.com/t/issues-with-inheritance/172375/3 "2009-07-20T17:51:01Z")

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Am Montag 20 Juli 2009 17:41:06 schrieb Juston Davies:

> ```
> super.execute "Batman?"
> 
> ```

You want super(“Batman”) here.  
super calls the superclass’s method of the same name as the current  
method  
with the same arguments as passed to the current method.  
super(args) calls the superclass’s method with the arguments specified  
So what your line does it calls the superclass’s method with the  
arguments  
passed to the current method and then calls execute on the result of  
that.

HTH,  
Sebastian

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<div class="post-metadata">

**Author:** ![Juston\_Davies](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e68b1a/32.png) [@Juston\_Davies](https://www.ruby-forum.com/u/Juston_Davies)\
**Post date:** [July 20, 2009, 5:51pm UTC](https://www.ruby-forum.com/t/issues-with-inheritance/172375/4 "2009-07-20T17:51:36Z")

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You nailed it. I tip my hat to you. I also figured out why child2  
looked like it invoking itself, that was a perception error on my  
part. Thanks!