CA1012: Abstract types should not have public constructors

Item Value
RuleId CA1012
Category Design
Fix is breaking or non-breaking Non-breaking

Cause

A type is abstract and has a public constructor.

By default, this rule only looks at externally visible types, but this is configurable.

Rule description

Constructors on abstract types can be called only by derived types. Because public constructors create instances of a type and you cannot create instances of an abstract type, an abstract type that has a public constructor is incorrectly designed.

How to fix violations

To fix a violation of this rule, either make the constructor protected or don't declare the type as abstract.

When to suppress warnings

Do not suppress a warning from this rule. The abstract type has a public constructor.

Suppress a warning

There are various ways to suppress a code analysis warning, including disabling the rule for the project, using a preprocessor directive to disable it for a specific line of code, or by applying the SuppressMessageAttribute attribute. For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following option to configure which parts of your codebase to run this rule on.

You can configure this option for just this rule, for all rules, or for all rules in this category (Design). For more information, see Code quality rule configuration options.

Include specific API surfaces

You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal

Example

The following code snippet contains an abstract type that violates this rule.

' Violates this rule      
Public MustInherit Class Book

    Public Sub New()
    End Sub

End Class
// Violates this rule
public abstract class Book
{
    public Book()
    {
    }
}

The following code snippet fixes the previous violation by changing the accessibility of the constructor from public to protected.

// Does not violate this rule
public abstract class Book
{
    protected Book()
    {
    }
}
' Violates this rule      
Public MustInherit Class Book

    Protected Sub New()
    End Sub

End Class