Exceptions: Difference between revisions

=={{header|Ruby}}==

===Defining an exception===

<ruby>class SillyError < Exception

def initialize(args = nil)

@args = args

end

end</ruby>

Note: Often new exceptions are defined simply with no body. For example:

<ruby>class MyInvalidArgument < ArgumentError

end</ruby>

This example makes "MyInvalidArgument" an type of ArgumentError (one of the built-in exceptions). It's simply declared as a subclass of the existing exception and no over-riding is necessary. (A rescue clause for ArgumentError would catch MyInvalidArgument exceptions ... but one's code could insert a more specific exception handler for the more specific type of exception).

===Throwing an exception===

<ruby>def spam

raise SillyError, 'egg'

end</ruby>

===Handling an exception===

rescue/else/ensure

<ruby>begin

foo

rescue SillyError, se

print se.args

bar()

else

# no exception occurred

quux

ensure

baz

end</ruby>

The "rescue" clause is like the "catch" clause in other languages. The "ensure" clause is like the "finally" clause in other languages.

===Catch/Throw===

Ruby has a separate exception-like system that is meant to be used to exit out of deep executions that are not errors.

<python>def foo

throw :done

end

catch :done do

foo

end</python>

You can only "throw" and "catch" symbols. Like exceptions, the throw can be made from a function defined elsewhere from the catch block.