Search code examples
crystal-lang

Scope variables/guards

Is it possible to have a variable that is guaranteed to be finalized on the scope exit.

Specifically, I want a guard: something that calls a specific function on initialization, and calls another specific function on scope exit.

Solution

  • This is best done explicitly:

    class Guard
  def initialize
    # Init things here
  end

  def close
    # clean up things here
  end
end

def my_method
  guard = Guard.new
  # do things here
ensure
  guard.close
end

    Then a common pattern is to provide a nicer interface using a yielding method. You'll notice you see this a lot in the standard library when working with external resources:

    class Guard
  def self.obtain
    guard = new
    yield guard
  ensure
    guard.close
  end

  # ...
end

Guard.obtain do |guard|
  # do things
end

    Of course yielding the actual resource object is optional if the consumer should never interact with it.