I have a class Player which has a variable @hitpoints in the initialize method. I have made the variable accessible by use of attr_accessor :hitpoints.
The variable is indeed accessible when an instance of the class Player is created. However, I would like to allow only writing of an integer to it. As of now, I can assign a string:
conan.hitpoints = "Hello there!"
Any idea how to accomplish this?
Another common practice is to convert the argument, e.g. using to_i:
def hitpoints=(value)
@hitpoints = value.to_i
end
10.to_i #=> 10
10.5.to_i #=> 10
"10".to_i #=> 10
"foo".to_i #=> 0
or Integer:
def hitpoints=(value)
@hitpoints = Integer(value)
end
Integer(10) #=> 10
Integer(10.5) #=> 10
Integer("10") #=> 10
Integer("foo") #=> ArgumentError: invalid value for Integer(): "foo"
Note that you don't necessarily have to type check your arguments. Ruby will raise an exception sooner or later if the object doesn't behave as expected:
health = 100
hitpoints = "foo"
health -= hitpoints #=> TypeError: String can't be coerced into Fixnum
You can write a custom setter for it:
class Player
attr_accessor :hitpoints
def hitpoints=(value)
raise 'Not an integer' unless value.is_a? Integer
@hitpoints = value
end
end
You should also use this setter in your initialization method instead of instance variable:
def initialize(hitpoints)
self.hitpoints = hitpoints
end
UPDATE:
About attr_accessor. This method defined both setter and getter method for an attribute. Because you are defining your own setter later in the code, the default one is not needed and may be discarded with attr_reader, as suggested in comments by Stefan and Arup.
I have pretty mixed feelings about this though, as if you were working with somebody else, he will firstly noticed attr_reader at the top of your class and will think - Hey, why is it a read_only attribute? If it is a new developer, it might even cause him to write some nonsense code.
I believe that the code is to show its purpose, hence I would use attr_accessor even if it gives me method redefined warning. This is however a matter of personal preference.
attr_accessor :hitpoints is still needed ?
attr_reader :hitpoints to avoid a method redefined warning
attr_accessor vs attr_readerattr_accessor declaration, assuming the class is using the default setter.