readme.md

Code Smell 160 - Invalid Id = 9999

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

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

#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

int main(void)
{    
    int id;
    id = get_value();
    if (id < 0) 
    { 
        printf("Error: Failed to obtain value\n");
        return EXIT_FAILURE;
    }  
    return id;
}  

int get_value() 
{
  // something bad happened
  return -1; // Return a negative value to indicate error
}

// No INVALID_VALUE defined

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

Code Smell 120 - Sequential IDs

Code Smell 12 - Null

Code Smell 208 - Null Island

More Info

Null: The Billion Dollar Mistake

Y2K22 - The Mistake That Embarrasses Us

Disclaimer

Code Smells are just my opinion.

Credits

Photo by Markus Spiske on Unsplash

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Bugs lurk in corners and congregate at boundaries.

Boris Beizer

Software Engineering Great Quotes

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This article is part of the CodeSmell Series.

How to Find the Stinky Parts of your Code