rspec/rules/S1118/csharp/rule.adoc

== Why is this an issue?

Utility classes, which are collections of https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/static[`static`] members, are not meant to be instantiated.

C# adds an implicit https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/public[`public`] https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/constructors[`constructor`] to every class which does not explicitly define at least one constructor. Hence, at least one https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/protected[`protected`] constructor should be defined if you wish to inherit this utility class. Or the `static` keyword should be added to the class declaration to prevent inheriting it.

== How to fix it

=== Code examples

==== Noncompliant code example

[source,csharp,diff-id=1,diff-type=noncompliant]
----
public class StringUtils // Noncompliant: implicit public constructor
{ 
  public static string Concatenate(string s1, string s2) 
  {
    return s1 + s2;
  }
}
----

or

[source,csharp,diff-id=2,diff-type=noncompliant]
----
public class StringUtils // Noncompliant: explicit public constructor
{ 
  public StringUtils()
  {
  }

  public static string Concatenate(string s1, string s2) 
  {
    return s1 + s2;
  }
}
----

==== Compliant solution

[source,csharp,diff-id=1,diff-type=compliant]
----
public static class StringUtils
{ 
  public static string Concatenate(string s1, string s2) 
  {
    return s1 + s2;
  }
}
----

or

[source,csharp,diff-id=2,diff-type=compliant]
----
public class StringUtils
{ 
  protected StringUtils()
  {
  }

  public static string Concatenate(string s1, string s2) 
  {
    return s1 + s2;
  }
}
----

== Resources

=== Documentation

* https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/static[Static keyword]
* https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/constructors[Constructors]
* https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/using-constructors[Using Constructors]
* https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/access-modifiers[Access Modifiers]

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Hide this public constructor by making it ["protected"|"private"].

Add a ["protected"|"private"] constructor or the "static" keyword to the class declaration.

'''
== Comments And Links
(visible only on this page)

=== on 24 Jun 2015, 14:09:33 Ann Campbell wrote:
very minor edits [~tamas.vajk]. Assigned to you for double-check

=== on 25 Jun 2015, 06:23:47 Tamas Vajk wrote:
\[~ann.campbell.2] thanks, it looks good.

=== on 25 Jun 2015, 17:39:51 Ann Campbell wrote:
\[~tamas.vajk] I noticed you overrode the SQALE remediation cost. Is this truly a language-specific difference, or do you think it's wrong in the main task?

=== on 26 Jun 2015, 06:24:39 Tamas Vajk wrote:
\[~ann.campbell.2] In Java you can write call a utility method through an instance, like ``++(new StringUtils()).Concatenate("a", "b")++``, so if you change the visibility of the constructor, then you'll need to change all these calls to ``++StringUtils.Concatenate(...)++``. However, in C# you can't use a static method through an instance, so changing the visibility of the constructor won't affect the code as much as in Java.

But thinking about it a bit, the 2 minutes is a bit too short, I'll modify it to 10mn, because you might have useless ``++new StringUtils()++`` calls in the code.

=== on 26 Jun 2015, 11:16:22 Ann Campbell wrote:
Okay [~tamas.vajk]

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]