Blocks are obviously very common in Ruby, and sometimes we use them to surround a certain piece of logic. A good example is transaction in ActiveRecord:

Season.transaction do
  update_attributes! name: 'fall'
  trees.update_all leaf_count: 0
end

Very nice to look at! A transaction is opened, then the block is run, then when the block completes, the transaction is closed.

One thing I wanted to point out that library developers need to watch out for is how the block interacts with return, which could potentially lead to undesiarable behavior. Imagine you had a reconfigure method like this, which breaks a connection while it reconfigures and then restarts when done:

# definition of block method
def reconfigure
  disconnect
  yield configuration # reconfigure
  reconnect
end

Dandy, but imagine it was used like this by a developer:

def start
  reconfigure do |c|
    c.user_name = 'seejohnrun'
    return if c.valid?

    # do something to make this valid
  end
end

The problem is that due to the way that the reconfigure function is written, the return will actually prevent the rest of reconfigure from running, and reconnect will never be called as the developer expected.

The way to fix this and keep it consistent, is with ensure, like so:

# definition of block method
def reconfigure
  disconnect
  yield configuration # reconfigure
ensure
  reconnect
end

Just something to keep in mind!

Back to the original transaction example for reference, check out the implementation of within_new_transaction (used by transaction): http://apidock.com/rails/v4.0.2/ActiveRecord/ConnectionAdapters/DatabaseStatements/within_new_transaction