k1gabi k1gabi - 1 year ago 100
C# Question

Implicit cast on reference type

I have the following code with the explicit cast

a = (Class2)o

using System;

class Class1 { }
class Class2 : Class1{ }

class IsTest
static void Test(object o)
Class1 a;
Class2 b;

if (o is Class2)
Console.WriteLine("o is Class2");
a = (Class2)o; // Works
a = o; // **implicit cast won't work - error CS0266**
static void Main()
Class1 c1 = new Class1();
Class2 c2 = new Class2();

When I'm trying to implicit cast a = o it gives me the error CS0266.
From what I know converting a reference type to a direct or indirect ancestor class is a widening conversion, so a program can make the conversion implicitly.

b is derived from a, so why the implicit cast doesn't work?

Answer Source

It is as per the C# standard:

Thus, conversion operators are not allowed to convert from or to object because implicit and explicit conversions already exist between object and all other types.


Additionally to that see all the possible implicit conversions defined in 13.1.4 Implicit reference conversions at the http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-334.pdf

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