我正在通过在线课程进行“课堂介绍”练习。目的是创建一个Calculator
用两个数字初始化的类。然后可以将数字相加,相减,相乘和相除。我的代码在本地环境中似乎可以正常工作:
class Calculator
def initialize(x,y)
@x, @y = x, y
end
def self.description
"Performs basic mathematical operations"
end
def add
@x + @y
end
def subtract
@x - @y
end
def multiply
@x * @y
end
def divide
@x.to_f/@y.to_f
end
end
但是该站点具有Rspec规格:
describe "Calculator" do
describe "description" do
it "returns a description string" do
Calculator.description.should == "Performs basic mathematical operations"
end
end
describe "instance methods" do
before { @calc = Calculator.new(7, 2) }
describe "initialize" do
it "takes two numbers" do
expect( @calc.x ).to eq(7)
expect( @calc.y ).to eq(2)
end
end
describe "add" do
it "adds the two numbers" do
expect( @calc.add ).to eq(9)
end
end
describe "subtract" do
it "subtracts the second from the first" do
expect( @calc.subtract ).to eq(5)
end
end
describe "multiply" do
it "should return a standard number of axles for any car" do
expect( @calc.multiply ).to eq(14)
end
end
describe "divide" do
it "divides the numbers, returning a 'Float' if appropriate" do
expect( @calc.divide ).to eq(3.5)
end
end
end
end
并且网站的规范抛出NoMethodError:
NoMethodError
undefined method `x' for #<Calculator:0x007feb61460b00 @x=7, @y=2>
exercise_spec.rb:14:in `block (4 levels) in <top (required)>'
只需添加此行
attr_reader :x, :y
这是更正的代码:
class Calculator
attr_reader :x, :y
def initialize(x,y)
@x, @y = x, y
end
def self.description
"Performs basic mathematical operations"
end
def add
# once you defined reader method as above you can simple use x to get the
# value of @x. Same is true for only y instead of @y.
x + y
end
def subtract
x - y
end
def multiply
x * y
end
def divide
x.to_f/y.to_f
end
end
看下面的规范代码:
describe "initialize" do
it "takes two numbers" do
expect( @calc.x ).to eq(7)
expect( @calc.y ).to eq(2)
end
#...
您正在致电@calc.x
和@calc.y
。但是您没有在类中定义任何名为as#x
和#y
as实例方法的方法Calculator
。这就是为什么您有非常明确的异常原因NoMethod error
。
当您编写时attr_reader :x, :y
,它将在内部为您创建这些方法。阅读这个答案,了解读者和作家方法在Ruby中。
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