Warns on class private constructors that are dead code

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Metadata

ID: csharp-best-practices/class-no-private-constructors

Language: C#

Severity: Warning

Category: Best Practices

Description

Classes with a private constructor can’t be instantiated outside of the class itself. Because they are unreachable, they should be removed or made public.

An exception is made for classes that access their own constructors (like a singleton), and classes that derive from System.Runtime.InteropServices.SafeHandle.

Non-Compliant Code Examples

class NonCompliant {
    private static int n1 = 1;
    private NonCompliant() { /* ... */ }
}

class NonCompliant : Test {
    private NonCompliant() { /* ... */ }
}

class NonCompliant {
    private static readonly Foo _foo = new Foo();
    private NonCompliant() { /* ... */ }
}

Compliant Code Examples

class Compliant {
    private NonCompliant() { /* ... */ }
    public static int n = 1;
}

class Compliant {
    public static int n1 = 1;
    public static int n2 = 2;
}

class Compliant {
    public Compliant() { /* ... */ }
}

class Compliant {
    private static readonly Compliant _singleton = new Compliant();
    private Compliant() { /* ... */ }
}

public sealed class CompliantEnum : SmartEnum<CompliantEnum> {
    public static readonly CompliantEnum One = new CompliantEnum(nameof(One), 1);
    private CompliantEnum(string name, int value) : base(name, value) {}
}

// Utility class
public static class Compliant {
    public static int Sum(int a, int b) { /* ... */ }
    private Compliant() { /* ... */ }
    public static int Value = 1;
}

class Compliant : SafeAccessTokenHandle {
    private Compliant() { /* ... */ }
}

class Compliant {
    private static readonly Compliant _singleton = new Compliant();
    public Compliant() { /* ... */ }
}