== Why is this an issue?

The https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/abstract[abstract] modifier in a class declaration is used to indicate that a class is intended only to be a base class of other classes, not instantiated on its own.

Since `abstract` classes cannot be instantiated, there is no need for `public` or `internal` constructors. If there is basic initialization logic that should run when an extending class instance is created, you can add it in a `private`, `private protected` or `protected` constructor.

== How to fix it

Restrict the constructor visibility to the minimum: `private`, `private protected` or `protected`, depending on the usage.

=== Code examples

==== Noncompliant code example

[source,csharp,diff-id=1,diff-type=noncompliant]
----
abstract class Base
{
    public Base() // Noncompliant: should be private, private protected or protected.
    {
      //...
    }
}
----

==== Compliant solution

[source,csharp,diff-id=1,diff-type=compliant]
----
abstract class Base
{
    protected Base()
    {
      //...
    }
}
----

== Resources

=== Documentation

* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/abstract[abstract keyword]
* https://en.wikipedia.org/wiki/Abstract_type[abstract type]

include::../rspecator.adoc[]