Code Smell 100 - GoTo

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)
}

Right

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.

Courtesy XKCD

Relations

Code Smell 12 - Null

Maxi Contieri ・ Oct 31 '20

#codenewbie #tutorial #oop

More Info

• Goto Statement considered harmful

• Wikipedia

Credits

Photo by Jens Johnsson on Unsplash

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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

Software Engineering Great Quotes

Maxi Contieri ・ Dec 28 '20

#codenewbie #programming #quotes #software

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This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code

Maxi Contieri ・ May 21 '21

#codenewbie #tutorial #codequality #beginners