Sometimes you need to guarantee that some processing is done at the
end of a block of code, regardless of whether an exception was raised.
For example, you may have a file open on entry to the block, and you
need to make sure it gets closed as the block exits.
The
ensure clause does just this.
ensure goes after the last
rescue clause and contains a chunk of code that will always be
executed as the block terminates. It doesn't matter if the block exits
normally, if it raises and rescues an exception, or if it is terminated
by an uncaught exception---the
ensure block will get run.
f = File.open("testfile")
begin
# .. process
rescue
# .. handle error
ensure
f.close unless f.nil?
end
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The
else
clause is a similar, although less useful, construct. If
present, it goes after the
rescue clauses and before any
ensure. The body of an
else clause is executed only if no
exceptions are raised by the main body of code.
f = File.open("testfile")
begin
# .. process
rescue
# .. handle error
else
puts "Congratulations-- no errors!"
ensure
f.close unless f.nil?
end
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