object_ids.rb

# Example 1
# to see the object ids when we have a variable shadowing

a = [1, 2, 3]

a.object_id # => 1960

a.map! do |a| 
  p a.object_id
  a + 1
end # 3
    # 5
    # 7

# 3,5,7 are the object ids of 1,2 and 3

a => [2, 3, 4] # we reassing each object with the +1 operation
a.object_id # => 1960

# As we can see we have the same array because have the same object id


# Example 2
# object_id when there is no variable shadowing

a = [1, 2, 3]
b = [4, 5, 6]

a.object_id # => 1960
b.object_id # => 1980

a.map! do |c| 
  p b.object_id
  c + 1
end # 1980
    # 1980
    # 1980

# the object_id 1980 is from returning 3 times `b` as the object array  

a => [2, 3, 4] # we also reassing each object with the +1 operation
a.object_id # => 1960
b.object_id # => 1980


# Example 3
# object_id with a mix of variable shadowing `b` & reassigment inside the block on `c`

a = ['a', 'b', 'c']
b = ['e', 'f', 'g']
c = ['x']

a.object_id # => 1820
b.object_id # => 1840
c.object_id # => 1850

a.each do|b| # as `b` is defined outside the scope `|b|`is shadowing this variable.
  p b  # `b` value is shadowing with `b` local variable, then we will have instead each object id of `a` array
  p a  # `a` value is the array itself ['a', 'b', 'c'] 
  c = ['h', 'i', 'j'] # as `a`, `c` is not shadowing and we can easily reassign it inside the block
  b = 'shadowing!' # local variable `b` is protected. We can't reassign `b` as `c`, ruby scopes this `b` shadowing in the block
end # "a"
    # ["a", "b", "c"]
    #  "b"
    # ["a", "b", "c"]
    # "c"
    # ["a", "b", "c"]

a # => ['a', 'b', 'c']
b # => ['e', 'f', 'g']
c # => ['h', 'i', 'j'] # as we can see, we re-wrote `c`
 
a.object_id # => 1820
b.object_id # => 1840
c.object_id # => 1880 # objet_id after `c` reassignment passed from `1850` to `1880`. It's another object!