No Nested Switch

ID

csharp.no_nested_switch

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

CSharp

Tags

control-flow, reliability, switch

Description

Reports a switch statement written inside another switch. The inner switch is reported once.

Rationale

A nested switch forces the reader to track two selector values and two sets of labels at the same time, and the inner break statements read as though they left the outer switch. The number of paths through the method is the product of the two label counts, so cases are easy to miss and hard to cover with tests.

public string Route(int kind, int code)
{
    switch (kind)
    {
        case 1:
            switch (code)             // FLAW — inner switch
            {
                case 10:
                    return "one-ten";
                default:
                    return "one";
            }
        default:
            return "other";
    }
}

public string RouteFlat(int kind, int code)
{
    switch (kind)                     // OK — the inner decision moved to its own method
    {
        case 1:
            return RouteKindOne(code);
        default:
            return "other";
    }
}

Remediation

Extract the inner switch into its own method named after the decision it makes, so each switch has a single selector and a single set of labels. When both selectors belong together, consider a switch on a tuple pattern ((kind, code) switch { …​ }) or a lookup table keyed by the pair.

References