Why is-a-role-of is one of the inheritance mistakes? - oop

Question

The illustration below is taken from my lecture slide. I've use both composition and inheritance to code a Student - Person class, I think both of them pretty reasonable.
(I know if One person can have many positions - 1:n , then inheritance doesn't work though, so I'm only taking about 1 person : 2 position relationship).
The code using Inheritance:
class Person
attr_accessor :name, :gender, :height, :weight
def initialize(name, gender, height, weight)
#name = name
#gender = gender
#height = height
#weight = weight
end
def cry
"woooo"
end
end
class Student < Person
attr_accessor :student_id
def initialize(name, gender, height, weight, student_id)
super(name, gender, height, weight)
#student_id = student_id
end
def study
"Student #{name} with #{student_id} is studying now"
end
end
s = Student.new("Lin", "Male", 173, 75, 666777)
puts s.cry()
puts s.study
Code using Composition:
class Person
attr_accessor :name, :gender, :height, :weight, :position
def initialize(name, gender, height, weight, position = nil)
#name = name
#gender = gender
#height = height
#weight = weight
#position = position
end
def cry
"woooo"
end
end
class Student
attr_accessor :student_id
def initialize(student_id)
#student_id = student_id
end
def study
"#{student_id} is studying now"
end
end
s = Student.new(666777)
p = Person.new("Lin", "Male", 173, 75, s)
puts p.cry()
puts p.position.study
And I found the code using composition has one bad side, I can't make student call he's name. I mean I can't make the study() method return something like the inheritance code does:
"Student #{name} with #{student_id} is studying now"