No Nonexistent Operator

ID

csharp.no_nonexistent_operator

Severity

high

Remediation Complexity

medium

Remediation Risk

low

Remediation Effort

medium

Resource

Code Smell

Language

CSharp

Tags

code_smell, suspicious-assignment, suspicious-operator

Description

Reports an assignment written as target =- num, target =+ num or target =! flag, where the = is glued to the unary operator that follows and the operand is set off by a space. C# has no =-, =+ or =! operator, so the layout claims something the code does not do.

Rationale

The compiler reads target =- num as "assign the negation of num to target`". A reader scanning the line sees the two glued characters as a single token and reads "subtract `num from target`" — the compound assignment `-=. Both readings are plausible, only one is what runs, and nothing in the build flags the difference. target =! flag is the same trap against !=: it overwrites target where a comparison was intended, and the result still type-checks whenever target is a bool.

This is a spacing defect rather than a structural one, so the rule uses token positions. The unary operator must begin exactly where the = ends, on the same line, and whitespace must separate it from its operand. Correctly spaced code (target = -num) and unambiguous tight code (target =-num) are both accepted.

public class Counter
{
    private int total;
    private bool active;

    public void Apply(int step, bool flag)
    {
        total =- step;        // FLAW — assigns -step; reads as total -= step
        total =+ step;        // FLAW — assigns +step; reads as total += step
        active =! flag;       // FLAW — assigns !flag; reads as active != flag

        total -= step;        // OK — real compound assignment
        total = -step;        // OK — spacing matches the meaning
        total =-step;         // OK — nothing to misread
    }
}

Remediation

Decide which of the two readings was meant. If the intent was to accumulate, use the compound assignment (total -= step). If the intent really was to assign a signed or inverted value, put a space after the = so the layout matches (total = -step). For the =! form, check whether a comparison (!=) was intended before changing anything.

References