This is an implementation of Daniel Berger's proposal of structured warnings for Ruby.
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This is an implementation of Daniel Berger's proposal of structured warnings for Ruby. They provide dynamic suppression and activation, as well as, an inheritance hierarchy to model their relations. This library preserves the old warn signature, but additionally allows a raise-like use.

For more information on the usage and benefits of this library have a look at the inspiring article at O'Reilly. (link to web archive - O'Reilly took it down)


Add this line to your application's Gemfile:

gem 'structured_warnings'

And then execute:

$ bundle

Or install it yourself as:

$ gem install structured_warnings


structured_warnings aims to work with all Ruby interpreters. Please file a bug for any incompatibilities.

Versions of structured_warnings before v0.3.0 are incompatible with Ruby 2.4+. Please upgrade accordingly, if you need Ruby 2.4 compatibility. Please note on the otherhand, that many class names changed in an incompatible way with structured_warnings v0.3.0. This was done to avoid future name clashes.

Here's a table which should ease upgrading.

v0.2.0 and before v0.3.0 and after
Warning StructuredWarnings::Base
StandardWarning StructuredWarnings::StandardWarning
DeprecationWarning StructuredWarnings::DeprecationWarning
DeprecatedMethodWarning StructuredWarnings::DeprecatedMethodWarning
DeprecatedSignatureWarning StructuredWarnings::DeprecatedSignatureWarning

Test framework support

structured_warnings supports both test-unit and minitest/test by adding the assert_warn and assert_no_warn assertions.

Pull requests which add support for RSpec or minitest/spec are very welcome.

Known Issues

In Ruby versions before 2.4, the library may not extend Ruby's built-in warnings handled by the C-level function rb_warn. Therefore warnings like "method redefined", "void context", and "parenthesis" may not be manipulated by structured_warnings.


To get you started - here is a short example

In order to use structured_warnings in library code, use the following code.

# in lib/...
require 'structured_warnings'

class Foo
  def old_method
    warn StructuredWarnings::DeprecatedMethodWarning, 'This method is deprecated. Use new_method instead'
    # Do stuff

# in test/...
require 'test/unit'
require 'structured_warnings'

class FooTests < Test::Unit::TestCase
  def setup
    @foo =

  def test_old_method_emits_deprecation_warning
    assert_warn(StructuredWarnings::DeprecatedMethodWarning){ @foo.old_method }

StructuredWarnings::DeprecatedMethodWarning is only one of multiple predefined warning types. You may add your own types by subclassing StructuredWarnings::Base if you like.

Client code of your library will look as follows:

require "foo"

foo =
foo.old_method # => will print
               # ... `old_method' : This method is deprecated. Use new_method instead (StructuredWarnings::DeprecatedMethodWarning)

But the main difference to the standard warning concept shipped with ruby, is that the client is able to selectively disable certain warnings s/he is aware of and not willing to fix.

StructuredWarnings::DeprecatedMethodWarning.disable # Globally disable warnings about deprecated methods!

foo.old_method # => will print nothing

StructuredWarnings::DeprecatedMethodWarning.enable # Reenable warnings again.

And there is an even more powerful option for your clients, the can selectively disable warnings in a dynamic block scope.

# Don't bug me about deprecated method warnings within this block, I know
# what I'm doing.
StructuredWarnings::DeprecatedMethodWarning.disable do

These settings are scoped to the local thread (and all threads spawned in the block scope) and automatically reset after the block.

Detailed Documentation

Have closer look at the RDoc of StructuredWarnings::Warning, StructuredWarnings::Base and StructuredWarnings::Base::ClassMethods.

Part of this library is a set of different warnings:

  • StructuredWarnings::Base
    • StructuredWarnings::BuiltInWarning
    • StructuredWarnings::StandardWarning
    • StructuredWarnings::DeprecationWarning
      • StructuredWarnings::DeprecatedMethodWarning
      • StructuredWarnings::DeprecatedSignatureWarning

You are encouraged to use your own subclasses of StructuredWarnings::Base to give as much feedback to your users as possible.



After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at


The gem is available as open source under the terms of the MIT License.