String Replace Ruby - ruby

Question

I am trying to play around my codes in ruby.
Here's what I got:
name = "Rol"
title = name
name = "Sam"
puts name
puts title
OUTPUT:
Sam
Rol
name = "Rol"
title = name
name.replace("Sam")
puts name
puts title
OUTPUT:
Sam
Sam
Basically I wondering why when I use reassignment equal sign it changes just the variable name and left the title with the old value. However upon using the replace method, it changes the value of both?
Any explanation in layman's term on this? Newbie in ruby here.

Answer 1

The simple layman terms are:
Assignments change variables.
Mutation methods change objects.
Variables and objects are different things in Ruby. Each variable is a label that points to an object. Each method call is sent to an object. For convenience we often simplify discussion, because it is easy to say "The name is 'Sam'" when in detail we mean "The value stored in the String object pointed to by the name variable is 'Sam'"
In your first example:
The line name = "Rol" creates a new String object from the literal "Rol" and points the local variable name at it.
The line title = name points the local variable title to the same String object.
The line name = "Sam" creates a new String object from the literal "Sam" and points the local variable name at it. Now name and title point to different String objects.
At this point there are two independent String variables, with two different variables pointing at them, so any uses of them remain separate.
In your second example:
The line name = "Rol" creates a new String object from the literal "Rol" and points the local variable name at it.
The line title = name points the local variable title to the same String object.
The line name.replace("Sam") modifies the object. It doesn't matter which variable you used to access the object in the first place. title.replace("Sam") would have identical results, since it refers to the same object.

Answer 2

The answer is very simple.
When you call:
title = name
then both variables: title and name have reference to the same object, which is next modified by:
name.replace("Sam")

Answer 3

String#replace replaces the content of the string referenced by name. However, it works at reference level as opposite to = that assigns a new String object to the left variable.
name is assigned to title, which means at that point in time both variables point to the same memory allocation. Since replace replaces the referenced string, the change is effectively propagated to both.
You get a better sense if you compare the object_id of the values. In the case of the assignment, the object ID changes because you effectively create and assign a new object:
name = "Rol"
title = name
name.object_id
# => 70336016119860
title.object_id
# => 70336016119860
name = "Sam"
name.object_id
# => 70336016085020
title.object_id
# => 70336016119860
For the case of replace, instead, the object_id doesn't change because you change the value directly without creating a new object.
name = "Rol"
title = name
name.object_id
# => 70336003479640
title.object_id
# => 70336003479640
name.replace("Sam")
name.object_id
# => 70336003479640
title.object_id
# => 70336003479640