如何判断Constant是否已定义在模块命名空间内，而不是全局的？
我有两个同名的常量；一个是全局常量，另一个是在命名空间 Admin 下定义的。但我需要区分它们；全局的已经定义了，作用域的如果尚未定义则需要自动定义：
A = 'A Global Const'
module Admin
A = 'A Const within the Admin namespace' if const_defined? 'A' # always true and the Admin::A can never be defined!
end
puts A # => 'A Global Const'
puts Admin::A # => NameError: uninitialized constant Admin::A
# the Admin::A will never be defined.
但是如果定义了全局A，则“const_defind？”部分将始终返回 ture！
我什至尝试过：
... if defined? A
... if self.const_defined? 'A'
... if Object.const_get('Admin').const_defined? 'A'
永远正确！
我需要区分它们，因为我需要使用 A 和 Admin::A 两种形式中的 A；
就像公共使用的 PostsController 和管理员使用的 Admin::PostsController 的情况；
帮助！
I have two Const with the same name; One is a global const, and the other is defined under the namespace Admin. But I need to distinguish them;The global one has already defined, and the scoped one need to auto defined if it has not been defined yet:
A = 'A Global Const'
module Admin
A = 'A Const within the Admin namespace' if const_defined? 'A' # always true and the Admin::A can never be defined!
end
puts A # => 'A Global Const'
puts Admin::A # => NameError: uninitialized constant Admin::A
# the Admin::A will never be defined.
But if the Global A is defined, the "const_defind?" part will always return ture!
I even have tried:
... if defined? A
... if self.const_defined? 'A'
... if Object.const_get('Admin').const_defined? 'A'
Always true!
I need to distinguish them because I need to use the A in A and Admin::A two forms;
Like the situation PostsController for public use, and Admin::PostsController for admin use;
Help!
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您应该尝试确定两者的范围以仅测试您想要的一个
You should try scoping both of them to test just the one you want
事实上，
const_define?和const_get遍历层次结构，对于模块来说包括(人为）Object类。不过，您可以使用 Module#constants 来避免这种情况：注意：在 Ruby 1.8 中，您检查的是
"A"，而不是:AIndeed,
const_defined?andconst_getgo through the hierarchy, which for modules include (artificially) theObjectclass. You can useModule#constantsto avoid this, though:Note: In Ruby 1.8, you check against
"A", not:A使用其
#class或#to_s或#inspect可以帮助您了解您定义的对象是否实际上是全局的。Using its
#classor#to_sor#inspectmay help you know if your defined object is actually global or not.