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Unnecessarily complex Boolean expression

ID: cs/simplifiable-boolean-expression
Kind: problem
Security severity: 
Severity: recommendation
Precision: high
Tags:
   - quality
   - maintainability
   - readability
Query suites:
   - csharp-code-quality.qls
   - csharp-security-and-quality.qls

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There are a number of Boolean expression patterns that can easily be rewritten to make them simpler. Boolean expressions involving comparisons with Boolean literals, ternary conditionals with a Boolean literal as one of the results, double negations, or negated comparisons can all be changed to equivalent and simpler expressions.

Recommendation

If A and B are expressions of Boolean type, you can simplify them using the rewrites shown below.

Expression		Simplified expression
A == true		A
A != false		A
A == false		!A
A != true		!A
A ? true : B		A || B
A ? B : false		A && B
A ? B : true		!A || B
A ? false : B		!A && B
A ? true : false		A
A ? false : true		!A
!!A		A
A && true		A
A || false		A

Some expressions always yield a constant value. If the side-effect in `A` is intended, consider restructuring the code to make this more clear. Otherwise, replace the expression with the constant value as shown below.

Expression		Value
A && false		false
A || true		true
A ? true : true		true
A ? false : false		false

In addition to the rewrites above, negated comparisons can also be simplified in the following way:

Expression		Simplified expression
!(A == B)		A != B
!(A != B)		A == B
!(A < B)		A >= B
!(A > B)		A <= B
!(A <= B)		A > B
!(A >= B)		A < B

Example

In the following example, the properties Espresso, Latte, and Grande are written in a complex way and can be simplified.

class Bad
{
    int Size { get; set; }

    bool Espresso => !(Size > 4);
    bool Latte => Espresso == false && Size <= 8;
    bool Grande => Espresso == false ? Latte != true : false;
}

The code below shows the same logic expressed in a simpler and more readable way.

class Good
{
    int Size { get; set; }

    bool Espresso => Size <= 4;
    bool Latte => !Espresso && Size <= 8;
    bool Grande => !Espresso && !Latte;
}

References

• Microsoft C# Reference: ! Operator, == Operator, != Operator, && Operator, || Operator, ?: Operator, < Operator.

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