String assignment by reference/copy?

Question

Can anyone explain the behavior

Scenario-1

str = "hello"
str1 = str
puts str #=> hello
puts str1 #=> hello

str1 = "hi"
puts str1 #=> hi
puts str #=> hello

Here, changing the value of str1 has no effect on the value of str.

Scenario-2

str = "hello"
str1 = str
str1.gsub! "hello", "whoa!"
puts str1 #=> whoa
puts str #=> whoa

Shoudn't the gsub! effect only the str1? Why is it changing str? If str1 just holds the reference to str, then why did the value not change in Scenario-1?

Answer 1

Look below carefully:

Scenario-1

str = "hello"
str1 = str
puts str #=> hello
puts str1 #=> hello
p str.object_id #=>15852348
p str1.object_id #=> 15852348

In the above case str and str1 holding the reference to the same object which is proved by the object_id. Now you use the local variable str1 in the below case to hold a new object "hi",which is also proved by the two different object_ids.

str1 = "hi"
puts str1 #=> hi
puts str #=> hello
p str.object_id  #=> 15852348
p str1.object_id #=> 15852300

Scenario-2

`String#gsub! says:

Performs the substitutions of String#gsub in place, returning str, or nil if no substitutions were performed. If no block and no replacement is given, an enumerator is returned instead.

str = "hello"
str1 = str
str1.gsub! "hello", "whoa!"
puts str1 #=> whoa
puts str #=> whoa
p str.object_id #=>16245792
p str1.object_id #=>16245792