Begin, Rescue and Ensure in Ruby?

Yes, ensure ensures that the code is always evaluated. That's why it's called ensure. So, it is equivalent to Java's and C#'s finally.

The general flow of begin/rescue/else/ensure/end looks like this:

begin  # something which might raise an exceptionrescue SomeExceptionClass => some_variable  # code that deals with some exceptionrescue SomeOtherException => some_other_variable  # code that deals with some other exceptionelse  # code that runs only if *no* exception was raisedensure  # ensure that this code always runs, no matter what  # does not change the final value of the blockend

You can leave out rescue, ensure or else. You can also leave out the variables in which case you won't be able to inspect the exception in your exception handling code. (Well, you can always use the global exception variable to access the last exception that was raised, but that's a little bit hacky.) And you can leave out the exception class, in which case all exceptions that inherit from StandardError will be caught. (Please note that this does not mean that all exceptions are caught, because there are exceptions which are instances of Exception but not StandardError. Mostly very severe exceptions that compromise the integrity of the program such as SystemStackError, NoMemoryError, SecurityError, NotImplementedError, LoadError, SyntaxError, ScriptError, Interrupt, SignalException or SystemExit.)

Some blocks form implicit exception blocks. For example, method definitions are implicitly also exception blocks, so instead of writing

def foo  begin    # ...  rescue    # ...  endend

you write just

def foo  # ...rescue  # ...end

or

def foo  # ...ensure  # ...end

The same applies to class definitions and module definitions.

However, in the specific case you are asking about, there is actually a much better idiom. In general, when you work with some resource which you need to clean up at the end, you do that by passing a block to a method which does all the cleanup for you. It's similar to a using block in C#, except that Ruby is actually powerful enough that you don't have to wait for the high priests of Microsoft to come down from the mountain and graciously change their compiler for you. In Ruby, you can just implement it yourself:

# This is what you want to do:File.open('myFile.txt', 'w') do |file|  file.puts contentend# And this is how you might implement it:def File.open(filename, mode='r', perm=nil, opt=nil)  yield filehandle = new(filename, mode, perm, opt)ensure  filehandle&.closeend

And what do you know: this is already available in the core library as File.open. But it is a general pattern that you can use in your own code as well, for implementing any kind of resource cleanup (à la using in C#) or transactions or whatever else you might think of.

The only case where this doesn't work, if acquiring and releasing the resource are distributed over different parts of the program. But if it is localized, as in your example, then you can easily use these resource blocks.

BTW: in modern C#, using is actually superfluous, because you can implement Ruby-style resource blocks yourself:

class File{    static T open<T>(string filename, string mode, Func<File, T> block)    {        var handle = new File(filename, mode);        try        {            return block(handle);        }        finally        {            handle.Dispose();        }    }}// Usage:File.open("myFile.txt", "w", (file) =>{    file.WriteLine(contents);});

FYI, even if an exception is re-raised in the rescue section, the ensure block will be executed before the code execution continues to the next exception handler. For instance:

begin  raise "Error!!"rescue  puts "test1"  raise # Reraise exceptionensure  puts "Ensure block"end

If you want to ensure a file is closed you should use the block form of File.open:

File.open("myFile.txt", "w") do |file|  begin    file << "#{content} \n"  rescue  #handle the error here  endend