introduction.md

Introduction

Casting and type conversion are different ways of changing an expression from one data type to another.

An expression can be cast to another type with the cast operator (<type>).

long l = 1000L;
int i = (int)l;

object o = new Random();
Random r = (Random)o;

If the types are not compatible an instance of InvalidCastException is thrown. In the case of numbers this indicates that the receiving type cannot represent the cast value. In the case of classes, one of the types must be derived from the other (this also applies trivially to structs).

An alternative to casting is type conversion using the is operator. This is typically applied to reference and nullable types.

object o = new Random();
if (o is Random rand)
{
    int ii = rand.Next();
    // now, do something random
}

If you need to detect the precise type of an object then is may be a little too permissive as it will return true for a class and any of the classes and interfaces from which it is derived directly or indirectly. typeof and Object.GetType() are the solution in this case.

object o = new List<int>();

o is ICollection<int> // true
o.GetType() == typeof(ICollection<int>) // false
o is List<int> // true
o.GetType() == typeof(List<int>) // true