访问类的常量变量

Question

当我有

class Foo
   CONSTANT_NAME = ["a", "b", "c"]

  ...
end

有没有办法访问Foo::CONSTANT_NAME或我必须使用类方法来访问该值？

Answer 1

你发布的内容应该是完美的:

class Foo
  CONSTANT_NAME = ["a", "b", "c"]
end

Foo::CONSTANT_NAME
# => ["a", "b", "c"]

Answer 2

如果您在类中编写包含常量的其他代码,则可以将其视为全局代码.

class Foo
  MY_CONSTANT = "hello"

  def bar
    MY_CONSTANT
  end
end

Foo.new.bar #=> hello

如果您在类外部访问常量,请在其前面加上类名,后跟两个冒号

Foo::MY_CONSTANT  #=> hello

Answer 3

一些替代品:

class Foo
  MY_CONSTANT = "hello"
end

Foo::MY_CONSTANT
# => "hello"

Foo.const_get :MY_CONSTANT
# => "hello"

x = Foo.new
x.class::MY_CONSTANT
# => "hello"

x.class.const_defined? :MY_CONSTANT
# => true

x.class.const_get :MY_CONSTANT
# => "hello"

Answer 4

有办法访问Foo::CONSTANT_NAME吗？

就在这里:

Foo::CONSTANT_NAME