I cannot see the value of the instance variable @model when I call the lambda @description. Is this possible? I only see " is very good." when I call show_description. Thanks in advance.
class Car
def initialize(model)
@model = model
end
def description
@description = lambda{yield}
end
def show_description
@description.call
end
end
c = Car.new("Ford")
c.description{"#{@model} is very good."}
puts c.show_description # => " is very good."
c.description{"#{@model} is very good."} wouldn't show you what you want. Point is, the block you passing, has access to the outside scope, where no variable @model is found, thus @model is nil. It is called encapsulation, due to this, outside world wouldn't be able to know/access directly the state of an object, in your case the object is c. Here object's state means value to the instance variables lies in object c. But using methods, you can read/update the states of the objects.
Thus do as c.description{"#{c.model} is very good."}.
Your code can be re-written as :
class Car
attr_reader :model
def initialize(model)
@model = model
end
def description
@description = yield
end
def show_description
@description
end
end
c = Car.new("Ford")
c.description{"#{c.model} is very good."}
puts c.show_description
# >> Ford is very good.
Since you are saving the proc instance as @description, it is better to access that via a variable rather than using yield.
def description &pr
@description = pr
end
You need to evaluate @description in the appropriate environment, i.e. within the instance of Car.
def show_description
instance_exec(&@description)
end
With the fixes as above, it will work as you intended.
c = Car.new("Ford")
c.description{"#{@model} is very good."}
puts c.show_description
# => Ford is very good.
By the way, you can simplify "#{@model} is very good." to "#@model is very good.".
cvar, gvar abd ivar don't need {..}, only # is enough. Example - >> @x = 12 => 12 >> "I have #@x pens" => "I have 12 pens"
You can do it like this:
class Car
attr_reader :model
def initialize(model)
@model = model
end
def description
@description = lambda{yield}
end
def show_description
@description.call
end
end
c = Car.new("Ford")
c.description{"#{c.model} is very good."}
puts c.show_description #Ford is very good.
