Parameter Shadows Property

csharp.parameter_shadows_property

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

CSharp

Description

Reports a method or constructor parameter whose name matches a property declared on the enclosing class. The parameter shadows the property in the body: any unqualified use of the name resolves to the parameter, and the property must be reached through this.X. Forgetting the qualifier silently reads or assigns the parameter when the property was meant.

Rationale

C# name resolution gives the local parameter priority over the enclosing-class property. The compiler does not warn, so a missing this. is invisible to the reader and produces wrong results at runtime — typically a property that "doesn’t update" or a constructor parameter that "doesn’t take effect".

public class Order
{
    public int Total { get; set; }

    public void Add(int Total)       // FLAW — Total shadows the property
    {
        Total = Total + 1;           // assigns the parameter, not the property
    }

    public void AddOk(int amount)    // OK — distinct name
    {
        Total = Total + amount;
    }

    public Order(int Total)          // OK — this.Total = Total is the canonical assign-from-param idiom
    {
        this.Total = Total;
    }
}

A constructor parameter is exempt when the constructor’s body assigns it straight to the same-named property (this.Total = Total;) — the shadow is resolved deliberately and correctly at that one line, so there is nothing to rename. The exemption is scoped to constructors: Add(int Total) above would keep being flagged even if it were rewritten as this.Total = Total;, because an ordinary method mixing a parameter with reads of the same property elsewhere is not the same shape as a constructor’s one-line initialisation.

Remediation

Rename the parameter so it cannot be confused with the property — the conventional camelCase parameter / PascalCase property split removes the collision and the need for a this. qualifier.

References

General naming conventions