CODEWITHSUNDEEP
rubysyntaxerror-handling
John F. Miller
John F. Miller

Reputation: 27217

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

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?

Upvotes: 41

Views: 32637

Answers (2)

pimpin
pimpin

Reputation: 297

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.

Upvotes: 13

klochner
klochner

Reputation: 8125

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.

Upvotes: 51

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