`var = something rescue nil` behaviour
In Ruby you can write a rescue
at the end of an assignment to catch any errors that might come up. I have a function (below: a_function_that_may_fail
) where it's convenient to let it throw an error if certain conditions aren't met. The following code works well
post = {}
# Other Hash stuff
post['Caption'] = a_function_that_may_fail rescue nil
However I'd like to have post['Caption'] not even set if the function fails.
I know I can do:
beg开发者_C百科in
post['Caption'] = a_function_that_may_fail
rescue
end
but that feels a little excessive - is there a simpler solution?
The problem is precedence. The simplest solution:
(post['Caption'] = a_function_that_may_fail) rescue nil
Changing the precedence like this is a little esoteric, though. It would probably be better if you can rewrite your a_function_that_may_fail
to return nil
if it fails.
You could also use a temporary variable and test for nilness:
caption = a_function_that_may_fail rescue nil
post['Caption'] = caption unless caption.nil?
A really minor difference is that this does not set post['Caption']
if a_function_that_may_fail
did not raise an exception but returned nil
.
post.store('Caption', a_function_that_may_fail) rescue nil
make sure your method returns either nil
or false
:
def this_may_fail
some_logic rescue nil
end
you can then use the if modifier to check the return value of your method and assign the value only if it's not nil
or false
:
post['Caption'] = this_may_fail if this_may_fail
or you can cache the return value of this_may_fail
in a local variable if you don't like to call the method twice for the if condition and assignment.
the_value = this_may_fail
post['Caption'] = the_value if the_value
also notice that the rescue
modifier only catches StandardError
and its subclasses.
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