Exception the good way to catch what you really need to catch

11 June 2014

This tip from Roman describes the common exceptions catching bad practice, which everyone should be aware of and avoid. When writing

begin
    ...
  rescue Exception => e
    ...
  end

you will catch all errors, including SyntaxError. This may be a real problem, and the broken code will run until some customer reports it. The example two files illustrate it:

bad_file.rb:

()(())

test.rb:

begin
  require 'bad_file'
rescue Exception => e
  puts "In rescue 1."
end

begin
  require 'bad_file'
rescue => e
  puts "In rescue 2."
end

When running test.rb, it prints:

In rescue 1.
test.rb:8:in `require': ./bad_file.rb:1: syntax error, unexpected '(', expecting $end (SyntaxError)
()(())
   ^
from test.rb:8

which proves that 'rescue Exception => e' style is dangerous and catches the error you would not want to be in the code.