Ruby-on-rails 访问类的常量
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Accessing a class's constants
提问by Jeremy Smith
When I have the following:
当我有以下内容时：
class Foo
CONSTANT_NAME = ["a", "b", "c"]
...
end
Is there a way to access with Foo::CONSTANT_NAMEor do I have to make a class method to access the value?
有没有办法访问Foo::CONSTANT_NAME或我必须创建一个类方法来访问该值？
回答by Dylan Markow
What you posted should work perfectly:
您发布的内容应该可以完美运行：
class Foo
CONSTANT_NAME = ["a", "b", "c"]
end
Foo::CONSTANT_NAME
# => ["a", "b", "c"]
回答by aidan
Some alternatives:
一些替代方案：
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"
回答by ma?ek
If you're writing additional code within your class that contains the constant, you can treat it like a global.
如果您在包含常量的类中编写附加代码，则可以将其视为全局变量。
class Foo
MY_CONSTANT = "hello"
def bar
MY_CONSTANT
end
end
Foo.new.bar #=> hello
If you're accessing the constant outside of the class, prefix it with the class name, followed by two colons
如果您在类之外访问常量，请使用类名作为前缀，后跟两个冒号
Foo::MY_CONSTANT #=> hello
回答by J?rg W Mittag
Is there a way to access
Foo::CONSTANT_NAME?
有办法访问
Foo::CONSTANT_NAME吗？
Yes, there is:
就在这里：
Foo::CONSTANT_NAME
