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?
2 Answers
You can only use rescue in two cases:
Within a
begin ... end
blockbegin 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
.
-
4
module
andclass
bodies are implicitbegin
blocks, too. Commented Mar 26, 2010 at 18:01 -
4@Jörg W Mittag: as are
do ... end
blocks anddef ... end
method definitions. IS there anything else that is an implicitbegin
?while
,case
, orif
for example? Commented Mar 28, 2010 at 1:24 -
7
-
I suggest adding the comment above about do...end to the answer... that is really what I was looking for.– pedzCommented Jul 26, 2017 at 15:51
-
6Although not very well documented, as of ruby 2.5
rescue
works in regulardo
/end
blocks (not in-line blocks{...}
though). commit Commented Feb 18, 2020 at 15:38
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.
-
1
do ... end
blocks can't be rescued from without an explicitbegin ... end
.do ... end
blocks can be rescued without an explicitbegin ... end
.