GOTO was considered harmful 50 years ago
TL;DR: Don't ever use GoTo.
Problems
Readability
Hard to follow code
Solutions
Replace GOTO with structured code
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
More Info
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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