Ruby：如何從包含模塊的類中訪問常量

Question

我正在嘗試訪問我在其中包含的模塊中的各個類中保持的常量。 作為一個基本的例子

module foo
  def do_something_to_const
    CONSTANT.each { ... do_something ... }
  end
end

class bar
  include foo

  CONSTANT = %w(I want to be able to access this in foo)
end

class baz
  include foo

  CONSTANT = %w(A different constant to access)
end

由於模塊的邏輯在多個類之間共享，我希望能夠僅引用常量（其名稱在每個類中保持相同，但內容不同）。 我該怎么做呢？

Answer 1

您可以將包含的類模塊引用為self.class並使用const_get或self.class::CONST ，后者稍快一些：

module M
  def foo
    self.class::CONST
  end
end

class A
  CONST = "AAAA"
  include M
end

class B
  CONST = "BBBB"
  include M
end

puts A.new.foo # => AAAA
puts B.new.foo # => BBBB

Answer 2

您可以使用self.class引用該類

module Foo
  def do_something
    self.class::Constant.each {|x| puts x}
  end
end

class Bar
  include Foo
  Constant = %w(Now is the time for all good men)
end

class Baz
  include Foo
  Constant = %w(to come to the aid of their country)
end

bar = Bar.new
bar.do_something
=>
Now
is
the
time
for
all
good
men
 => ["Now", "is", "the", "time", "for", "all", "good", "men"] 

baz = Baz.new
baz.do_something
=>
to
come
to
the
aid
of
their
country
 => ["to", "come", "to", "the", "aid", "of", "their", "country"]

Answer 3

您可以使用::運算符將CONSTANT范圍CONSTANT為BAR類。 語法看起來像這樣：

module Foo
  def do_something_to_const
    Bar::CONSTANT.each { |item| puts item }
  end
end

class Bar
  include Foo

  CONSTANT = %w(I want to be able to access this in foo)
end

Bar.new.do_something_to_const # outputs each item in Bar::CONSTANT

不過，我會盡量避免這種情況。 包含的模塊不需要知道包含它的類的實現細節。