When comparing to booleans, we perform magic castings and get unexpected results.

TL;DR: Don't compare against true. Either you are true, or false or you shouldn't compare

Problems

• Hidden castings

• The least surprise principle violation.

• Fail Fast principle violation

Solutions

1. Use booleans

2. Don't mix booleans with boolean castable obejcts

Context

Many languages cast values to boolean crossing domains.

Sample Code

Wrong

#!/bin/bash

if [ false ]; then
    echo "True"
else
    echo "False"
fi

# this evaluates to true since 
# "false" is a non-empty string


if [ false ] = true; then
    echo "True"
else
    echo "False"
fi

# this also evaluates to true

Right

#!/bin/bash

if  false ; then
    echo "True"
else
    echo "False"
fi

# this evaluates to false

Detection

[X] Automatic

Linters can check for explicit comparisons and warnings.

Tags

• Castings

Conclusion

It is a common industry practice to use many non booleans as booleans.

We should be very strict when using booleans.

Relations

More Info

Credits

Photo by Michael Held on Unsplash

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If it doesn’t work, it doesn’t matter how fast it doesn’t work.

Mich Ravera

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This article is part of the CodeSmell Series.