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Clean code, jump free (Example in Lua)

The "goto" statement - in languages that still support it - is regarded with disdain by Computer Scientists as it makes for spaghetti code - hard to follow and going all over the place!

In some ways, loop controls "break" and "continue" ("last", "next" and "redo" in Perl; "next", "redo", "retry" and "break" in Ruby) are also forms of the goto. They are not as bad in that they only jump within a limited area, but on the other hand many forms don't involve labels so that there's no clue at the destination point in your code that it's an arrival point.

Having slagged off these statements (and in reality I'm being a pedantic computer scientist by doing so - I use them personally from time to time!) I had better off you the alternative. Written on yesterday's Lua course as a demonstration - here's a while loop that has an ugly break in it ...

j=14
while 1 do
  print (j)
  if j > 20 then break end
  j = j + 1
end
print ("done")


... and here's the alternative using a control variable. ...

j=14
running = true
while running do
  print (j)
  if j > 20 then
    running = false
  else
    j = j + 1
  end
end
print ("done")


That code being longer, but purer and easier to maintain.
(written 2008-08-06, updated 2008-08-07)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
R104 - Ruby - Control Structures
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  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2619] Passing code to procedures and yield in Ruby - (2010-02-02)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2287] Learning to program in Ruby - examples of the programming basics - (2009-07-15)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [1891] Ruby to access web services - (2008-11-16)
  [1887] Ruby Programming Course - Saturday and Sunday - (2008-11-16)
  [1870] What to do with a huge crop of apples - (2008-11-04)
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  [995] Ruby's case - no break - (2006-12-17)
  [985] Equality in Ruby - == eql? and equal? - (2006-12-14)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [960] 1st, 2nd, 3rd revisited in Ruby - (2006-12-02)

U103 - Lua - Conditionals and loops
  [3686] The goto statement in Lua - (2012-04-06)
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [2455] Lua examples - coroutines, error handling, objects, etc - (2009-10-15)
  [2454] For loops in Lua - (2009-10-14)
  [2351] Ternary operators alternatives - Perl and Lua lazy operators - (2009-08-12)
  [1685] Short circuit evaluation (lazy operator) in Lua - (2008-06-22)


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