在Ruby中，如何从类的实例中调用类方法?说我有
class Truck
def self.default_make
# Class method.
"mac"
end
def initialize
# Instance method.
Truck.default_make # gets the default via the class's method.
# But: I wish to avoid mentioning Truck. Seems I'm repeating myself.
end
end
Truck.default_make行检索默认值。但有办法不提卡车吗?似乎应该有。
当前回答
类似于你的问题，你可以用:
class Truck
def default_make
# Do something
end
def initialize
super
self.default_make
end
end
其他回答
类似于你的问题，你可以用:
class Truck
def default_make
# Do something
end
def initialize
super
self.default_make
end
end
你做得对。类方法(类似于c++或Java中的“静态”方法)不是实例的一部分，因此必须直接引用它们。
关于这一点，在你的例子中，你最好将'default_make'设置为常规方法:
#!/usr/bin/ruby
class Truck
def default_make
# Class method.
"mac"
end
def initialize
# Instance method.
puts default_make # gets the default via the class's method.
end
end
myTruck = Truck.new()
类方法对于使用该类的实用程序类型函数更有用。例如:
#!/usr/bin/ruby
class Truck
attr_accessor :make
def default_make
# Class method.
"mac"
end
def self.buildTrucks(make, count)
truckArray = []
(1..count).each do
truckArray << Truck.new(make)
end
return truckArray
end
def initialize(make = nil)
if( make == nil )
@make = default_make()
else
@make = make
end
end
end
myTrucks = Truck.buildTrucks("Yotota", 4)
myTrucks.each do |truck|
puts truck.make
end
在实例方法中，你可以直接调用self.class.whatever，而不是引用类的字面名称。
class Foo
def self.some_class_method
puts self
end
def some_instance_method
self.class.some_class_method
end
end
print "Class method: "
Foo.some_class_method
print "Instance method: "
Foo.new.some_instance_method
输出:
Class method: Foo Instance method: Foo
一个:
class Truck
def self.default_make
"mac"
end
attr_reader :make
private define_method :default_make, &method(:default_make)
def initialize(make = default_make)
@make = make
end
end
puts Truck.new.make # => mac
要访问实例方法中的类方法，请执行以下操作:
self.class.default_make
这里有一个解决你的问题的替代方案:
class Truck
attr_accessor :make, :year
def self.default_make
"Toyota"
end
def make
@make || self.class.default_make
end
def initialize(make=nil, year=nil)
self.year, self.make = year, make
end
end
现在让我们使用我们的类:
t = Truck.new("Honda", 2000)
t.make
# => "Honda"
t.year
# => "2000"
t = Truck.new
t.make
# => "Toyota"
t.year
# => nil
