Unnecessarily complex Boolean expression¶

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

Click to see the query in the CodeQL repository

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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