How to mark a class as Deprecated in Ruby?

Question

In Ruby (and even more so: Rails) it is easy to mark methods as deprecated.

But how can I mark an entire class as deprecated? I want to raise a warning whenever a class is used:

class BillingMethod
end

BillingMethod.new #=> DEPRECATION WARNING: the class BillingMethod is deprecated. Use PaymentMethod instead.

Or when it gets used in inheritance:

class Sofort < BillingMethod
end

Sofort.new #=> DEPRECATION WARNING: the class BillingMethod is deprecated. Use PaymentMethod instead.

Or, when used in nested classes:

class BillingMethod::Sofort < BillingMethod
end

BillingMethod::Sofort.new #=> DEPRECATION WARNING: the class BillingMethod is deprecated. Use PaymentMethod instead.

I would think that a class_eval-block would be the place where to stick such a warning. Is that the correct place? Or are there better methods?

score 11 · Answer 1 · edited Oct 15 '19 at 12:16

11

You may want to have a look at Deprecate which is part of Ruby's Standard Library:

require 'rubygems'

class BillingMethod
  extend Gem::Deprecate

  class << self
    deprecate :new, "PaymentMethod.new", 2016, 4
  end

  # Will be removed April 2016, use `PaymentMethod.new` instead
  def initialize 
    #...
  end
end

Using the deprecated method would result in a warning like this:

BillingMethod.new
# => NOTE: BillingMethod#new is deprecated; use PaymentMethod.new instead. It will be removed on or after 2016-04-01.
# => BillingMethod#new called from file_name.rb:32.

edited Oct 15 '19 at 12:16

3limin4t0r

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answered Apr 17 '15 at 11:05

spickermann

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1

That will only raise warnings when an object gets initialized. Not when a class is used as parent or used in a nested class tree. Or am I missing an important detail? – berkes Apr 17 '15 at 11:07
@berkes You can use the above to deprecate the `inherited` hook (class method), thereby deprecating inheritance: `class BillingMethod; class << self; deprecate :inherited, :none, 2016, 4; end; end`. Inheriting from BillingMethod should now issue the deprecation warning. – Petr Skocik Apr 17 '15 at 11:21
The code in the example is wrong. Because `:new` is a class-method, you need to wrap the `extend...deprecate` lines in a `class << self` block. – berkes Apr 17 '15 at 11:54
@berkes, I fixed my example. – spickermann Apr 17 '15 at 13:25

Andrey Deineko · Accepted Answer · 2015-12-14T19:01:05.390

5

You can use const_missing to deprecate constants, and, by extension, classes.

const_missing is being invoked when an undefined constant is referenced.

module MyModule

  class PaymentMethod
    # ...
  end

  def self.const_missing(const_name)
    super unless const_name == :BillingMethod
    warn "DEPRECATION WARNING: the class MyModule::BillingMethod is deprecated. Use MyModule::PaymentMethod instead."
    PaymentMethod
  end
end

This allows existing code that references MyModule::BillingMethod to continue to work, and warns the user about their use of the deprecated class.

It's the best I've seen so far for the deprecating class purpose.

edited Dec 14 '15 at 19:01

answered Apr 17 '15 at 10:09

Andrey Deineko

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In your example, how would `const_missing` be fired, when you've defined it just above? – berkes Apr 17 '15 at 10:38
@berkes the first part should not be there, typo – Andrey Deineko Apr 17 '15 at 10:41
In the `const_missing` method, what is the `PaymentMethod\n end` exactly achieving there? – berkes Apr 17 '15 at 10:44
1

`const_missing` is being invoked when a reference is made to an undefined constant in module. It returns a value (`PaymentMethod` in this case) to be used for that constant. – Andrey Deineko Apr 17 '15 at 10:53
It seems to me, that the last `end` just before closing the `const_missing` -method is superflous and incorrect. In Ruby 2.1.x it gives a syntax error. – berkes Apr 17 '15 at 10:58

score -2 · Answer 3 · answered Apr 17 '15 at 10:04

-2

Why not do it this way:

def initialize(*args)
  warn "DEPRECATION WARNING: ..."
  super
end

answered Apr 17 '15 at 10:04

Gena Shumilkin

713
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Author wants to show warning on all class usages (e.g. inheritance), not only new objects creating. – hedgesky Apr 17 '15 at 10:31

How to mark a class as Deprecated in Ruby?

3 Answers3