return_safe_yield

Provides helpers for dealing with return statements in blocks and procs by either disallowing them or else ensuring that some code runs after yielding

Installation

Add this line to your application's Gemfile:

gem 'return_safe_yield'

And then execute:

$ bundle

Or install it yourself as:

$ gem install return_safe_yield

Usage

The problem

Consider the following code:

def some_method(&block)
  puts 1
  yield
  puts 3
end

def test
  some_method do
    puts 2
    return
  end
end

test

In this case, our return statement exits not only the method test, but also the method some_method. The line puts 3 is never called.

This is standard ruby behaviour. It lies in a block's responsibility to not use return if the actual block caller does not support it.

But what if you're not in control of the code that actually calls your block, and you don't know if it's safe to use return? And, on the other hand, what if you're writing 'black box' library code that accepts blocks or procs and does not handle returns in there well?

For this reason, this Gem provides two different methods for dealing with return statements in blocks.

Note that this implementation is a bit controversal, as there is a variety of skilled ruby developers thinking that the responsibility always lies with a block's or proc's author and no special handling should be performed. So if you're using this library, please make sure you absolutely need it in your case.

See this StackOverflow question for an interesting discussion of this subject.

Handle return statements gracefully

The first solution provided by this Gem is the method ReturnSafeYield.call_then_yield. It contains a very simple begin ... rescue ... ensure construct and can be passed two blocks. The second block is always executed unless the first block fails, even if the first block contains a return statement.

Use it as follows:

unknown_block = proc do
  return
end

ReturnSafeYield.call_then_yield(unknown_block) do
  # => This line is called even though the above block contains a `return`.
end

# => This line is still not called as the `return` statement exits the current
#    method context.

You can also pass arguments to the first block:

unknown_block = proc do |arg1, arg2|
end

ReturnSafeYield.call_then_yield(unknown_block, 'arg1 value', 'arg2 value') do
end

The second block receives the first block's return value as arguments (this does not apply if return is used explicitely):

unknown_block = proc
  'return value'
end

ReturnSafeYield.call_then_yield(unknown_block) do |arg1|
  arg1 == 'return value' # => true
end

Fail if block / proc contains return

The second approach offered by this Gem is the method safe_yield. It makes sure the given block does not contain a return statement. If it does, an ReturnSafeYield::UnexpectedReturnException exception is thrown.

Use it as follows:

unknown_block = proc do |some_argument|
  return
end

ReturnSafeYield.safe_yield(unknown_block, some_argument)
# => Raises an ReturnSafeYield::UnexpectedReturnException exception

This is the rigorous way of handling it and its use is controversial among a variety of rubyists.

Development

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 rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/remofritzsche/return_safe_yield. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Changelog

Unreleased

• Update dev-dependencies to mitigate vulnerabilities

0.2.1

• Fix returning arrays (previously, only first element was returned)

0.2.0

• Rescue all exceptions inheriting from Exception

Until 0.1.3

• Undocumented releases

License

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