How to implement Ruby utility class methods? - ruby

Question

Need help implementing Ruby utility class methods to get this test to pass. Can someone break this down for me please?
My Code
class Temperature
class << self
def from_fahrenheit temp
Temperature.new({f: temp})
end
def from_celsius temp
Temperature.new({c: temp})
end
end
def initialize(options={})
#f = options[:f]
#c = options[:c]
end
def in_fahrenheit
return #f if #f
(#c * (9.0 / 5.0)) + 32
end
def in_celsius
return #c if #c
(#f - 32) * 5.0 / 9.0
end
end
class Celsius < Temperature
def initialize temp
#temp = temp
end
end
class Fahrenheit < Temperature
def initialize temp
#temp = temp
end
end
Failures:
1) Temperature Temperature subclasses Celsius subclass is constructed in degrees celsius
Failure/Error: (#f - 32) * 5.0 / 9.0
NoMethodError:
undefined method `-' for nil:NilClass
# ./ct.rb:1118:in `in_celsius'
# ./ct.rb:1219:in `block (4 levels) in <top (required)>'
2) Temperature Temperature subclasses Fahrenheit subclass is constructed in degrees fahrenheit
Failure/Error: (#c * (9.0 / 5.0)) + 32
NoMethodError:
undefined method `*' for nil:NilClass
# ./ct.rb:1113:in `in_fahrenheit'
# ./ct.rb:1230:in `block (4 levels) in <top (required)>'
Rspec Test
describe "utility class methods" do
end
# Here's another way to solve the problem!
describe "Temperature subclasses" do
describe "Celsius subclass" do
it "is constructed in degrees celsius" do
Celsius.new(50).in_celsius.should == 50
Celsius.new(50).in_fahrenheit.should == 122
end
it "is a Temperature subclass" do
Celsius.new(0).should be_a(Temperature)
end
end
describe "Fahrenheit subclass" do
it "is constructed in degrees fahrenheit" do
Fahrenheit.new(50).in_fahrenheit.should == 50
Fahrenheit.new(50).in_celsius.should == 10
end
it "is a Temperature subclass" do
Fahrenheit.new(0).should be_a(Temperature)
end
end
end
end

Answer 1

You aren't using the Temperature class how you defined it. You take an options hash with :f and :c keys in it in the Temperature class, but don't set those in your sub-classes.
Try this:
class Celsius < Temperature
def initialize temp
super(c: temp)
end
end
class Fahrenheit < Temperature
def initialize temp
super(f: temp)
end
end
Is this for an exercise or something? It's an ... interesting design.