Code Smell 100 - GoTo

Code Smell 100 - GoTo

Maxi Contieri

Published on Nov 6, 2021

2 min read

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GOTO was considered harmful 50 years ago

TL;DR: Don't ever use GoTo.

Problems

  • Readability

  • Hard to follow code

Solutions

  1. Replace GOTO with structured code

  2. Use exceptions

Context

I started programming in Basic.

GOTO was heavily abused there.

I had to learn structured programming from scratch in Rehab mode.

Sample Code

Wrong

for x < 0 {
    if x > -1e-09 {
      goto small
    }
    z = z / x
    x = x + 1
  }
  for x < 2 {
    if x < 1e-09 {
      goto small
    }
    z = z / x
    x = x + 1
  }

  if x == 2 {
    return z
  }

  x = x - 2
  p = (((((x*_gamP[0]+_gamP[1])*x+_gamP[2])*x+_gamP[3])*x+_gamP[4])*x+_gamP[5])*x + _gamP[6]
  q = ((((((x*_gamQ[0]+_gamQ[1])*x+_gamQ[2])*x+_gamQ[3])*x+_gamQ[4])*x+_gamQ[5])*x+_gamQ[6])*x + _gamQ[7]
  return z * p / q

small:
  if x == 0 {
    return Inf(1)
  }
  return z / ((1 + Euler*x) * x)
}
for x < 0 {
    if x > -1e-09 {
      return small(x, z)
    }
    z = z / x
    x = x + 1
  }
  for x < 2 {
    if x < 1e-09 {
      return small(x, z)
    }
    z = z / x
    x = x + 1
  }

  if x == 2 {
    return z
  }

  x = x - 2
  p = (((((x*_gamP[0]+_gamP[1])*x+_gamP[2])*x+_gamP[3])*x+_gamP[4])*x+_gamP[5])*x + _gamP[6]
  q = ((((((x*_gamQ[0]+_gamQ[1])*x+_gamQ[2])*x+_gamQ[3])*x+_gamQ[4])*x+_gamQ[5])*x+_gamQ[6])*x + _gamQ[7]
  return z * p / q

small(x, z){
  if x == 0 {
     return Inf(1)
   }
   return z / ((1 + Euler*x) * x)
 }
}

Detection

[X] Automatic

In languages supporting GOTO, our linters can warn us against its usage.

Tags

  • Readability

Conclusion

We acknowledged GOTO problems a few decades ago.

The problem is still present in modern languages.

Most programmers luckily avoid GOTO sentence. Next goal will be to consider harmful null usage.

goto.png

Courtesy XKCD

Relations

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Credits

Photo by Jens Johnsson on Unsplash


It is practically impossible to teach good programming to students that have had a prior exposure to BASIC: as potential programmers they are mentally mutilated beyond hope of regeneration.

Edsger Dijkstra


This article is part of the CodeSmell Series.

 
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