Ruby Exceptions — Why “else”

exception handlingruby

I'm trying to understand exceptions in Ruby but I'm a little confused. The tutorial I'm using says that if an exception occurs that does not match any of the exceptions identified by the rescue statements, you can use an "else" to catch it:

begin  
# -  
rescue OneTypeOfException  
# -  
rescue AnotherTypeOfException  
# -  
else  
# Other exceptions
ensure
# Always will be executed
end

However, I also saw later in the tutorial "rescue" being used without an exception specified:

begin
    file = open("/unexistant_file")
    if file
         puts "File opened successfully"
    end
rescue
    file = STDIN
end
print file, "==", STDIN, "\n"

If you can do this, then do I ever need to use else? Or can I just use a generic rescue at the end like this?

begin  
# -  
rescue OneTypeOfException  
# -  
rescue AnotherTypeOfException  
# -  
rescue
# Other exceptions
ensure
# Always will be executed
end

Best Answer

The else is for when the block completes without an exception thrown. The ensure is run whether the block completes successfully or not. Example:

begin
  puts "Hello, world!"
rescue
  puts "rescue"
else
  puts "else"
ensure
  puts "ensure"
end

This will print Hello, world!, then else, then ensure.

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