Iterate over only public Ruby constants
Since Ruby 2.0 or so, it's been possible to make a constant private using private_constant , resulting in an error if the constant is used directly outside the declaring module.
However, constants and const_defined? still return private constants, and const_get allows access to them. Is there a way to programmatically identify private constants and filter them out at run time?
(Note: What does Module.private_constant do? Is there a way to list only private constants? and its answer don't specifically address this case, but rather the reverse (how to list only private constants).)
Update: It looks as though in Ruby 1.9 and 2.0, constants did include only public constants. As of 2.1, the no-arg constants still includes only public constants, but setting inherit to false with constants(false) (ie, list only constants defined in this module, not in its ancestor modules) has the side effect of exposing the private constants.
您可以通过下面的方式识别常量：
class A
C = "value"
private_constant :C
C2 = "value2"
end
A.constants #public constants
#=> [:C2]
A.constants(false) #public & private constants
#=> [:C, :C2]
A.constants(false) - A.constants #private constants
#=> [:C]
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