Code Smell 160 - Invalid Id = 9999

Photo by Markus Spiske on Unsplash

Code Smell 160 - Invalid Id = 9999

Maxint is a very good number for an invalid ID. We will never reach it.

Maxi Contieri
·Aug 30, 2022·

2 min read

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Table of contents

  • Problems
  • Solutions
  • Context
  • Sample Code
  • Detection
  • Tags
  • Conclusion
  • Relations
  • More Info
  • Disclaimer
  • Credits

TL;DR: Don't couple real IDs with invalid ones. In fact: Avoid IDs.

Problems

  • Bijection violation

  • You might reach the invalid ID sooner than your think

  • Don't use nulls for invalid IDs either

  • Coupling flags from caller to functions

Solutions

  1. Model special cases with special objects.

  2. Avoid 9999, -1, and 0 since they are valid domain objects and implementation coupling.

  3. Introduce Null Object

Context

In the early days of computing, data types were strict.

Then we invented The billion-dollar mistake.

Then we grew up and model special scenarios with polymorphic special values.

Sample Code

Wrong

#include "stdio.h"
#include "stdlib.h"
#include "stdbool.h"
#define INVALID_VALUE 999

int main(void)
{    
    int id = get_value();
    if (id==INVALID_VALUE)
    { 
        return EXIT_FAILURE;  
        // id is a flag and also a valid domain value        
    }
    return id;
}

int get_value() 
{
  // something bad happened
  return INVALID_VALUE;
}

// returns EXIT_FAILURE (1)

Right

#include "stdio.h"
#include "stdlib.h"
#include "stdbool.h"
// No INVALID_VALUE defined

int main(void)
{    
    int id;
    id = get_value();
    if (!id) 
    { 
        return EXIT_FAILURE;
        // Sadly, C Programming Language has no exceptions
    }  
    return id;
}  

get_value() 
{
  // something bad happened
  return false;
}

// returns EXIT_FAILURE (1)

Detection

[X] Semi-Automatic

We can check for special constants and special values on the code.

Tags

  • Null

Conclusion

We should use numbers to relate to the external identifiers.

If no external identifier exists, then it is not a number.

Relations

More Info

Disclaimer

Code Smells are just my opinion.

Credits

Photo by Markus Spiske on Unsplash


Bugs lurk in corners and congregate at boundaries.

Boris Beizer


This article is part of the CodeSmell Series.

 
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