The foreach
statement was introduced in the C# language prior to generics to make it easier to work with the non-generic collections available at that time such
as ArrayList. The foreach statements allow you to
downcast elements of a collection of Objects to any other type.
The problem is that to achieve the cast, the foreach statements silently perform explicit type
conversion, which at runtime can result in an InvalidCastException.
C# code iterating on generic collections or arrays should not rely on foreach statement’s silent explicit
conversions.
public class Fruit { }
public class Orange : Fruit { }
public class Apple : Fruit { }
class MyTest
{
public void Test()
{
var fruitBasket = new List<Fruit>();
fruitBasket.Add(new Orange());
fruitBasket.Add(new Orange());
fruitBasket.Add(new Apple());
foreach (Orange orange in fruitBasket) // Noncompliant
{
//...
}
}
}
public class Fruit { }
public class Orange : Fruit { }
public class Apple : Fruit { }
class MyTest
{
public void Test()
{
var fruitBasket = new List<Fruit>();
fruitBasket.Add(new Orange());
fruitBasket.Add(new Orange());
fruitBasket.Add(new Apple());
foreach (Orange orange in fruitBasket.OfType<Orange>())
{
//...
}
}
}
Exceptions
The rule ignores iterations on collections of objects. This includes legacy code that uses ArrayList. Furthermore, the
rule does not report on cases when user-defined conversions are being called.
