Method Could Be Static

csharp.method_could_be_static

Severity

info

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Efficiency

Language

CSharp

Description

Reports a private instance method that never touches instance state — no this, no base, and no unqualified reference to an instance field, property or method of the enclosing class. Such a method does not need an instance and can be declared static.

Rationale

A method that ignores instance state is conceptually a free function. Marking it static documents that it has no per-instance dependency, lets the compiler and JIT skip the implicit this argument, and makes the method callable and testable without constructing the type. The rule is deliberately limited to private methods so that making it static never changes a type’s public contract, an override, or an interface implementation.

The rule also skips every method of a class that declares a base type, or that is partial. In both cases, an unqualified name in the visible source may resolve to a member this single-compilation-unit analysis cannot see — an inherited member, or a member declared in another part of the partial class (typically generated designer/XAML code-behind that is not in source control). A named-control field like MyMap in a XAML view’s code-behind is a common example: it looks unresolved here, but flagging the method static would not compile.

public class Calculator
{
    private int factor = 2;

    // FLAW — uses only its parameters, no instance state
    private int Add(int a, int b) => a + b;
    private int Square(int x) => x * x;          // FLAW — could be static

    // OK — reads the instance field 'factor'
    private int Scale(int x) => x * factor;

    // OK — already static
    private static int Triple(int x) => x * 3;
}

Remediation

Add the static modifier to the method. If the method later needs instance state, the modifier can simply be removed again.

References

static (C# reference)