Don't call Enumerable.Cast<T> or Enumerable.OfType<T> with incompatible types
Don't call Enumerable.Cast<T> or Enumerable.OfType<T> with incompatible types
Microsoft docsDescription
System.Linq.Enumerable.Cast`1(System.Collections.IEnumerable) and System.Linq.Enumerable.OfType`1(System.Collections.IEnumerable) require compatible types to produce the expected result:
- The generic cast used by the sequence returned by System.Linq.Enumerable.Cast``1(System.Collections.IEnumerable) throws an System.InvalidCastException at runtime on elements of incompatible types.
- The generic type check used by System.Linq.Enumerable.OfType``1(System.Collections.IEnumerable) won't succeed with elements of incompatible types, resulting in an empty sequence.
Widening and user-defined conversions aren't supported with generic types.
Cause
A call to System.Linq.Enumerable.Cast`1(System.Collections.IEnumerable) or System.Linq.Enumerable.OfType`1(System.Collections.IEnumerable) specifies a type parameter that's incompatible with the type of the input collection.
How to fix violations
Use a compatible type for the type parameter of System.Linq.Enumerable.Cast`1(System.Collections.IEnumerable) and System.Linq.Enumerable.OfType`1(System.Collections.IEnumerable).
Example
var foods = new List<Food>();
// Violation - Food is incompatible with Beverages.
var drinks = Enumerable.Cast<Beverages>(foods);
// Violation - Food is incompatible with Beverages.
var drinks2 = Enumerable.OfType<Beverages>(foods);
class Food { }
class Bread : Food { }
class Beverages { }
var foods = new List<Food>();
// Bread is compatible with Food.
var breads = Enumerable.Cast<Bread>(foods);
// Bread is compatible with Food.
var breads2 = Enumerable.OfType<Bread>(foods);
class Food { }
class Bread : Food { }
class Beverages { }When to suppress
You shouldn't suppress warnings from this rule, as you'll either encounter runtime exceptions or unexpected behavior (empty sequences).