In Ruby, What structures can a `rescue` statement be nested in

Question

In ruby to catch an error one uses the rescue statement. generally this statement occurs between begin and end. One can also use a rescue statement as part of a block (do ... end) or a method (def ... end). My question is what other structures (loop, while, if, ...) if any will rescue nest within?

Answer 1

You can only use rescue in two cases:

• Within a begin ... end block

  begin   raise rescue    nil end 

• As a statement modifier

  i = raise rescue nil 

Function, module, and class bodies (thanks Jörg) are implicit begin...end blocks, so you can rescue within any function without an explicit begin/end.

    def foo       raise     rescue       nil     end 

The block form takes an optional list of parameters, specifying which exceptions (and descendants) to rescue:

    begin       eval string     rescue SyntaxError, NameError => boom       print "String doesn't compile: " + boom     rescue StandardError => bang       print "Error running script: " + bang     end 

If called inline as a statement modifier, or without argument within a begin/end block, rescue will catch StandardError and its descendants.

Here's the 1.9 documentation on rescue.

Answer 2

As said in recent comment, response has changed since Ruby 2.5.

do ... end blocks are now implicit begin ... end blocks; like module, class and method bodies.

In-line blocks {...} still can't.