Question

I’ve defined a Person class (name, age). I’ve tried to overload += operator on the @age instance variable, but I did not manage. Here my script attempt :

class Person

    def initialize(name, age)
        @name = name
        @age = age
    end

    def age+= (value)
        @age += value
    end

    def to_s
        return "I'm #{@name} and I'm #{@age} years old."
    end
end

laurent = Person.new "Laurent", 32
puts laurent
laurent.age += 2
puts laurent

And this the error I’ve got in terminal :

person.rb:8: syntax error, unexpected tOP_ASGN, expecting ';' or '\n'
    def age+= (value)
             ^
person.rb:15: syntax error, unexpected keyword_end, expecting $end

So, what’s wrong ?

Thanks in advance. And sorry if this may be a too obvious question.

Answer 1

You have to define + operator instead and you get += automatically.

But in this case you don’t need to override the + operator. The age member is just a number, so it already has everything defined. What you’re missing is a attr_accessor.

class Person
    attr_accessor :age

    def initialize(name, age)
        @name = name
        @age = age
    end

    def to_s
        return "I'm #{@name} and I'm #{@age} years old."
    end
end

laurent = Person.new "Laurent", 32
puts laurent
laurent.age += 2
puts laurent

You only need to override the + operator in case you want your class to behave like a number and be able to add to it directly like this:

laurent = Person.new "Laurent", 32
laurent += 2

But is not very readable in my opinion in this case.