如何在 Ruby 中定义 class 级常量正则表达式以供外部 classes 使用

Question

我正在编写一些测试来验证要在 Ruby 控制台应用程序中使用的某些正则表达式的行为。我正在尝试在不打算实例化的 class 上定义常量 class 级别字段（只是应该在其上定义常量 RE 值。我无法使用 [=37 正确定义它=] 习语（我有 C++/C# 背景）。

首先我尝试定义一个class常量

class Expressions
  # error is on following line (undefined method DATE)
  Expressions.DATE = /(?<Year>\d{4})-(?<Month>\d{2})-(?<Day>\d{2})/

end

class MyTest < Test::Unit::TestCase
  def setup
    @expression = Expressions::DATE
  end

  def test
    assert "1970-01-01" =~ @expression
  end
end

这只会产生错误：Expressions:Class (NoMethodError)

的未定义方法“DATE=”

接下来我尝试了class属性：

class Expressions
  @@Expressions.DATE = /(?<Year>\d{4})-(?<Month>\d{2})-(?<Day>\d{2})/ 
end

class MyTest < Test::Unit::TestCase
  def setup
    # NameError: uninitialized constant Expressions::DATE here:
    @expression = Expressions::DATE
  end

  def test
    assert "1970-01-01" =~ @expression
  end
end

这会产生一个 NameError: uninitialized constant Expressions::DATE 错误。

我知道我可以在 class 上定义属性以用作实例，但这是低效的并且不是解决问题的正确方法（只是一个技巧）。（在 C++ 中我会使用静态常量，完成）

所以我真的卡住了。我需要知道在 Ruby 中定义需要在其他 class 中使用的常量正则表达式的正确方法是什么。我对定义、初始化及其使用有疑问，

谢谢。

Answer 1

A constant in Ruby is like a variable, except that its value is supposed to remain constant for the duration of a program. The Ruby interpreter does not actually enforce the constancy of constants, but it does issue a warning if a program changes the value of a constant. Lexically, the names of constants look like the names of local variables, except that they begin with a capital letter. By convention, most constants are written in all uppercase with underscores to separate words, LIKE_THIS. Ruby class and module names are also constants, but they are conventionally written using initial capital letters and camel case, LikeThis.

The Ruby Programming Language: David Flanagan; Yukihiro Matsumoto.

这应该有效：

class Expressions
  DATE = /.../
end

class MyTest < Test::Unit::TestCase
  def setup
    @expression = Expressions::DATE
  end
  # ...
end

如何在 Ruby 中定义 class 级常量正则表达式以供外部 classes 使用

How to define class level constant regular expressions in Ruby to be used by external classes

ruby

regex

constants