Hi all, I need help understanding part of my code. I'm learning about data
structures, at the moment binary search tree.
This code does what I want, but I don't understand return statement in
insert
method. Why @root = root works as it works. If i put last line just root,
global variable root is nil instead of tree filled with nodes.
Here is my code:
class BinarySearchTree
class Node
attr_accessor :value, :left_child, :right_child
def initialize(value)
@value = value
@left_child = nil
@right_child = nil
end
end
attr_accessor :root
def initialize()
@root = nil
end
def insert(root = @root, value)
if root == nil
root = Node.new(value)
elsif value <= root.value
root.left_child = insert(root.left_child, value)
else
root.right_child = insert(root.right_child, value)
end
@root = root #works with this return statement
#root <- doesn't work with this statement, why!!!
end
end
x = BinarySearchTree.new()
x.insert(15)
x.insert(10)
p x.root
In your method #insert, root is just a variable. Putting `root` as the last statement in #insert will return the value of that variable from the #insert method.
But it won’t set the @root attribute on the class, which is what you are reading when you say `p x.root`. @root is an attribute on the class BinarySearchTree; root is a variable in the insert method. They are not the same thing.
I suspect you need to go back and learn some more about classes and attributes – sorry.
···
From: ruby-talk [mailto:ruby-talk-bounces@ruby-lang.org] On Behalf Of Igor Maljkovic
Sent: 12 December 2018 10:08
To: ruby-talk@ruby-lang.org
Subject: not understanding return statement
Hi all, I need help understanding part of my code. I'm learning about data structures, at the moment binary search tree.
This code does what I want, but I don't understand return statement in insert
method. Why @root = root works as it works. If i put last line just root,
global variable root is nil instead of tree filled with nodes.
Here is my code:
class BinarySearchTree
class Node
attr_accessor :value, :left_child, :right_child
def initialize(value)
@value = value
@left_child = nil
@right_child = nil
end
end
attr_accessor :root
def initialize()
@root = nil
end
def insert(root = @root, value)
if root == nil
root = Node.new(value)
elsif value <= root.value
root.left_child = insert(root.left_child, value)
else
root.right_child = insert(root.right_child, value)
end
@root = root #works with this return statement
#root <- doesn't work with this statement, why!!!
end
end
x = BinarySearchTree.new()
x.insert(15)
x.insert(10)
p x.root
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If you want to see a working implementation of binary search trees in Ruby,
you may want to take a look at this:
Also, for other data structures:
Take a look at those posts first, and let me know if you need some help.
~ Ale Miralles.
···
On Wed, 12 Dec 2018 at 08:16, Andy Jones <Andy.Jones@jameshall.co.uk> wrote:
In your method #insert, root is just a variable. Putting `root` as the
last statement in #insert will return the value of that variable *from
the #insert method*.
But it won’t set the @root attribute on the class, which is what you are
reading when you say `p x.root`. @root is an attribute on the class
BinarySearchTree; root is a variable in the insert method. They are not the
same thing.
I suspect you need to go back and learn some more about classes and
attributes – sorry.
*From:* ruby-talk [mailto:ruby-talk-bounces@ruby-lang.org] *On Behalf Of *Igor
Maljkovic
*Sent:* 12 December 2018 10:08
*To:* ruby-talk@ruby-lang.org
*Subject:* not understanding return statement
Hi all, I need help understanding part of my code. I'm learning about data
structures, at the moment binary search tree.
This code does what I want, but I don't understand return statement in
insert
method. Why @root = root works as it works. If i put last line just root,
global variable root is nil instead of tree filled with nodes.
Here is my code:
class *BinarySearchTree*
class *Node*
attr_accessor :value, :left_child, :right_child
def initialize(*value*)
@value = value
@left_child = nil
@right_child = nil
end
end
attr_accessor :root
def initialize()
@root = nil
end
def insert(*root* = @root, *value*)
if root == nil
root = *Node*.new(value)
elsif value <= root.value
root.left_child = insert(root.left_child, value)
else
root.right_child = insert(root.right_child, value)
end
@root = root #works with this return statement
#root <- doesn't work with this statement, why!!!
end
end
x = *BinarySearchTree*.new()
x.insert(15)
x.insert(10)
p x.root
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To be fair, having @root (from class Foo) == foo.root, where "root" in
class Foo does *not*, is somewhat counterintuitive. I think it's a most
excellent thing, but it does lead to confusion among those learning
about attr_* useage.
$.02,
-Ken
···
On 2018-12-12 06:15, Andy Jones wrote:
But it won't set the @root attribute on the class, which is what you are reading when you say `p x.root`. @root is an attribute on the class BinarySearchTree; root is a variable in the insert method. They are not the same thing.
@root is the same as BinarySearchTree.root
In your insert method you are not returning something but assigning the
instance of your BinarySearchTree.root the value of the internal variable
root.
If you want to use a return statement you can just use ‘root’ at the end
but you have to change the line where you call the insert method.
x.root = x.insert(15)
I don’t recommend this but I hope you understand a little better what is
happening in your code.
PS: Read about classes, instances and attributes. Especially attributes.
···
On Wed, Dec 12, 2018 at 13:33 Ale Miralles <amiralles.net@gmail.com> wrote:
If you want to see a working implementation of binary search trees in
Ruby, you may want to take a look at this:
Mastering data structures in Ruby — AVL Trees | by Ale Miralles | amiralles | Medium
Also, for other data structures:
amiralles - Medium
Take a look at those posts first, and let me know if you need some help.
~ Ale Miralles.
On Wed, 12 Dec 2018 at 08:16, Andy Jones <Andy.Jones@jameshall.co.uk> > wrote:
In your method #insert, root is just a variable. Putting `root` as the
last statement in #insert will return the value of that variable *from
the #insert method*.
But it won’t set the @root attribute on the class, which is what you are
reading when you say `p x.root`. @root is an attribute on the class
BinarySearchTree; root is a variable in the insert method. They are not the
same thing.
I suspect you need to go back and learn some more about classes and
attributes – sorry.
*From:* ruby-talk [mailto:ruby-talk-bounces@ruby-lang.org] *On Behalf Of
*Igor Maljkovic
*Sent:* 12 December 2018 10:08
*To:* ruby-talk@ruby-lang.org
*Subject:* not understanding return statement
Hi all, I need help understanding part of my code. I'm learning about
data structures, at the moment binary search tree.
This code does what I want, but I don't understand return statement in
insert
method. Why @root = root works as it works. If i put last line just root,
global variable root is nil instead of tree filled with nodes.
Here is my code:
class *BinarySearchTree*
class *Node*
attr_accessor :value, :left_child, :right_child
def initialize(*value*)
@value = value
@left_child = nil
@right_child = nil
end
end
attr_accessor :root
def initialize()
@root = nil
end
def insert(*root* = @root, *value*)
if root == nil
root = *Node*.new(value)
elsif value <= root.value
root.left_child = insert(root.left_child, value)
else
root.right_child = insert(root.right_child, value)
end
@root = root #works with this return statement
#root <- doesn't work with this statement, why!!!
end
end
x = *BinarySearchTree*.new()
x.insert(15)
x.insert(10)
p x.root
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To be fair, having @root (from class Foo) == foo.root, where "root" in class Foo does *not*, is somewhat counterintuitive. I think it's a most excellent thing, but it does lead to confusion among those learning about attr_* useage.
Honestly, it’s not really counterintuitive unless you expect a variable to magically become an attribute, and frankly if they did, that would be _more_ confusing.
Again: `root` is just a variable. It’s private to the object. `@root` is an attribute, which _can_ be public to the object.
If you have a basic understanding of what a class is and what an attribute is, then this is the easy bit.
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