rspec/rules/S1944/csharp/rule.adoc

== Why is this an issue?

Inappropriate casts are issues that will lead to unexpected behavior or runtime errors, such as `InvalidCastException`s. The compiler will catch bad casts from one class to another, but not bad casts to interfaces.

It is much better to use the `as` operator because it will return `null` instead of throwing an exception.

=== Noncompliant code example

[source,csharp]
----
public interface IMyInterface
{ /* ... */ }

public class Implementer : IMyInterface
{ /* ... */ }

public class MyClass
{ /* ... */ }

public static class Program
{
  public static void Main()
  {
    var myclass = new MyClass();
    var x = (IMyInterface) myclass;     // Noncompliant, InvalidCastException is being thrown
    var b = myclass is IMyInterface;    // Noncompliant, always false
  }
}
----

=== Compliant solution

[source,csharp]
----
public interface IMyInterface
{ /* ... */ }

public class Implementer : IMyInterface
{ /* ... */ }

public class MyClass
{ /* ... */ }

public static class Program
{
  public static void Main()
  {
    var myclass = new MyClass();
    var x = myclass as IMyInterface;    // Compliant, but will always be null
    var b = false;
  }
}
----

=== Exceptions

No issue is reported if the interface has no implementing class in the assembly.

include::../see.adoc[]

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

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

=== Message

* Review this cast; in this project there's no type that implements both "{0}" and "{1}".
* Review this cast; in this project there's no type that extends "{0}" and implements "{1}".
* Nullable is known to be empty, this cast throws an exception.


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

=== on 11 Dec 2015, 08:58:50 Tamas Vajk wrote:
\[~ann.campbell.2] applied some changes to the description

=== on 11 Dec 2015, 13:57:58 Ann Campbell wrote:
looks good

=== on 21 Jul 2016, 14:39:03 Ann Campbell wrote:
\[~tamas.vajk] I've tweaked the wording of your addition. Please double-check me.

=== on 21 Jul 2016, 15:24:29 Tamas Vajk wrote:
\[~ann.campbell.2] "known-empty" is strange for me, I would probably go with simply "empty" if the original variant was not good.

=== on 21 Jul 2016, 15:38:42 Ann Campbell wrote:
Second attempt made [~tamas.vajk]

=== on 21 Jul 2016, 15:41:08 Tamas Vajk wrote:
\[~ann.campbell.2] perfect, thanks.

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

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