Object identity in ruby

Object Equality in Ruby

There are many methods to compare various objects like ‘eql?’, ‘==’, ‘===’, ‘equal? Methods.

eql? vs == vs === Methods

In ruby, all the classes inherit from the Object class either directly or indirectly. This leads to the object equality logic between the basic object class and kernel module.

Below is the example that uses all the three methods mentioned above for equality checking:

class Hello; end
class World < Hello; end
class Dummy; end

 
hello = Hello.new
world = World.new
dummy = Dummy.new

 
hello == hello # => true
hello == world # => false
hello == dummy # => false

 
hello.eql? hello # => true
hello.eql? world # => false
hello.eql? dummy # => false

 
hello === hello # => true
hello === world # => false
world === hello # => false
hello === dummy # => false

The kernel #=== Method

This method mainly uses check equality in case statements. Any class which can provide meaningful schematics can easily override this method.

For example, it is used in string classes for the override.

The Basic Object #== Method

Most of the core classes in ruby override this method. This method is more particular in some cases due to its property of more permissiveness for object comparison.

For example, the integer class uses this method to override and compare the objects if they are numerically equal or not. 

For this, 1 and 1.0 are numerically equal rather than the fact first one is an integer, and the other is a float.

The Kernel #eql? Method

This will check the quality of two objects by checking their hash key. If they both refer to the same hash key, then it returns true otherwise, false.

To determine the uniqueness of a member, we can use the hash instances.

Let’s understand this with the help of an example:

key = 'key'
other_key = 'key'
key.hash       # => -7531521849152071378
other_key.hash # => -7531521849152071378

 
key.object_id       # => 15935377035880
other_key.object_id # => 15935377028960

 
h = {}

 
h[key] = 'key'
h[other_key] = 'other key'

 
h # => { "key" => "other key" }

Here the other_key and key are two distinct instances.

This method return equality based on the values returned by the hash function. The hash method returns an integer, and we have the same value. In this case, we have the same value for both instances. This means we can override the value contained in the hash entry.

The equal? Method

It is used to verify object identity. It verifies that x is the same object as y. So it is not advised to override this method. Indeed the other three methods that we have learned, like ‘eql?’, ‘==’, ‘===’ are designed to be overridden in object class. The only method that is used to check equality in object iD is equal? Method.

Frequently Asked Questions

Name some of the operators that are used in Ruby.

Some of the operators used in Ruby are Arithmetic, Bitwise, Unary, Ternary, Logical, etc.

What is the use of Ruby Methods?

They prevent us from writing the same code many times in a program. You can refer to them as functions in other programming languages.

How can we use Ruby Methods?

You first need to define them using the def and end keywords. And make sure always to start the method name with a lowercase letter.

What do you understand by Ruby Strings?

Ruby strings manipulate and hold the typical sequence of bytes.

What is the use of global variables in ruby?

You can access the global variable anywhere in the entire program. They can be used with the ‘$’ symbol.

Conclusion

In this article, we have extensively discussed object and its id property and the need for object_id in detail with examples in support of the statements mentioned in the blog, followed by object equality in Ruby with various methods and their proper explanations with examples and the use cases.

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