User Guide #25 - Ruby - Exception processing: ensure

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There may be cleanup work that is necessary when a method finishes its work. Perhaps an open file should be closed, buffered data should be flushed, etc. If there were always only one exit point for each method, we could confidently put our cleanup code in one place and know that it would be executed; however, a method might return from several places, or our intended cleanup code might be unexpectedly skipped because of an exception.

begin
  file = open("/tmp/some_file", "w")
  # ... write to the file ...
  file.close
end

In the above, if an exception occurred during the section of code where we were writing to the file, the file would be left open. And we don't want to resort to this kind of redundancy:

begin
  file = open("/tmp/some_file", "w")
  # ... write to the file ...
  file.close
rescue
  file.close
  fail # raise an exception
end

It's clumsy, and gets out of hand when the code gets more complicated because we have to deal with every

return

break

For this reason we add another keyword to the "

begin...rescue...end

ensure

ensure

begin

begin
  file = open("/tmp/some_file", "w")
  # ... write to the file ...
rescue
  # ... handle the exceptions ...
ensure
  file.close   # ... and this always happens.
end

It is possible to use

ensure

rescue

begin...end

rescue

ensure