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Struct Vs Classes Messages   Related Types This message was discovered on microsoft.public.dotnet.languages.csharp. Responses highlighted in red are from those people who are likely to be able to contribute good, authoratitive information to this discussion. They include Microsoft employees, MVP's and others who IMHO contribute well to these kinds of discussions. Post a new message to this list... Ashish Sheth Hi Gurus, In C# why struct can't be inherited from another struct, just like a class can be inherited from another class? another question is all struct by default are inherited from System.Object class, how this is possible when it is not allowed to derive a struct from a class? and System.Object is the reference type provided by the .NET Framework then why structs are value types? since the struct are derived from System.Object then they should be also a reference type. Can anybody answer this questions? thanks and regards, Ashish Sheth Reply to this message...        Tom Porterfield Ashish Sheth wrote: [Original message clipped] Your logic is flawed. Numeric types such as int and decimal also derive from System.Object, so following your logic an int should be a reference type and should be allowed to derive from a class or be derived from. As structs are value types, unlike classes they do not require heap allocation. Also, as value types they cannot be derived from. Structs can implement an interface. -- Tom Porterfield Reply to this message...        Nicholas Paldino [.NET/C# MVP] (VIP) Ashish, A structure is a special case type in .NET, and is considered to have certain semantics. Also, structures are derived from ValueType, not Object (but ValueType is derived from Object). Hope this helps. -- - Nicholas Paldino [.NET/C# MVP] - Click here to reveal e-mail address "Ashish Sheth" <Click here to reveal e-mail address> wrote in message news:Click here to reveal e-mail address... [Original message clipped] Reply to this message...        Daniel Jin (VIP) "Nicholas Paldino [.NET/C# MVP]" wrote: [Original message clipped] as an interesting side note, System.ValueType itself is in fact not a value type. Reply to this message...        Jon Skeet [C# MVP] (VIP) Daniel Jin <Click here to reveal e-mail address> wrote: [Original message clipped] As another interesting side note, the value types themselves don't inherit from System.ValueType, either. Instead, their corresponding boxed types inherit from ValueType, and they don't inherit from anything. It's a murky world out there... -- Jon Skeet - <Click here to reveal e-mail address> http://www.pobox.com/~skeet If replying to the group, please do not mail me too Reply to this message...        Mike Schilling "Jon Skeet [C# MVP]" <Click here to reveal e-mail address> wrote in message news:Click here to reveal e-mail address... [Original message clipped] Can you enlarge on that? Consider: int i = 12; Object o = i; int j = (int)o; While it's clear that boxing and unboxing are taking place, it's not obviuous (to me, now) that type conversion is taking place as well. Reply to this message...        Jon Skeet [C# MVP] (VIP) Mike Schilling <Click here to reveal e-mail address> wrote: [Original message clipped] It is, because the boxed type isn't the same as the value type. Boxing and unboxing themselves are conversions. This is hidden at any number of levels from the developer, to be honest, but if you look at the CLI spec it's all there. Just don't expect to come out again with your mind in tact :) -- Jon Skeet - <Click here to reveal e-mail address> http://www.pobox.com/~skeet If replying to the group, please do not mail me too Reply to this message...        Mike Schilling "Jon Skeet [C# MVP]" <Click here to reveal e-mail address> wrote in message news:Click here to reveal e-mail address... [Original message clipped] Here's another program. public static void Main() { int i = 12; Object o = (Object)i; Console.WriteLine(i.GetType()); Console.WriteLine(i.GetType().BaseType); Console.WriteLine(i.GetType().GetHashCode()); Console.WriteLine(o.GetType()); Console.WriteLine(0.GetType().BaseType); Console.WriteLine(o.GetType().GetHashCode()); Console.WriteLine(i.GetType() == o.GetType()); } Its output is: System.Int32 System.ValueType 113273860 System.Int32 System.ValueType 113273860 True This doesn't disprove what you said, of course, it shows only that GetType() on an unboxed object returns the boxed type, or conversely that GetType() on a boxed object returns the unboxed type, which thereupon lies about its ancestry. Once dishonesty enters the type system, it's difficult to know who to believe:-) Reply to this message...        Jon Skeet [C# MVP] (VIP) Mike Schilling <Click here to reveal e-mail address> wrote: [Original message clipped] Well exactly. Most people don't really *need* to know that the the type system has two different representations, etc - GetType() and the like smudge the issue, but in a way which is arguably more useful than a precise but hard-to-work-with set of methods. The spec, however, needs to be a lot more precise, and is. -- Jon Skeet - <Click here to reveal e-mail address> http://www.pobox.com/~skeet If replying to the group, please do not mail me too Reply to this message...        Joe Mayo [C# MVP] (VIP) Hi Ashish, In addition to what the other people said, there is a concept called Type System Unification, which allows everything to be treated as an object. It kind of gives you the best of all worlds with the benefits of performance with struct/value types and the power of object-oriented programming with reference types. I discuss it more in the following article: http://www.csharp-station.com/Articles/ObjectClass.aspx BTW, comments on this article are welcome. Joe -- Joe Mayo, Author/Instructor Need C#/.NET training? visit www.mayosoftware.com C# Tutorial - www.csharp-station.com "Ashish Sheth" <Click here to reveal e-mail address> wrote in message news:Click here to reveal e-mail address... [Original message clipped] Reply to this message...        Mike Schilling "Joe Mayo [C# MVP]" <Click here to reveal e-mail address> wrote in message news:Click here to reveal e-mail address... [Original message clipped] (cough, cough, cough) That is, it makes different tradeoffs than do systems that distinguish objects from scalar types. Reply to this message...        Joe Mayo [C# MVP] (VIP) "Mike Schilling" <Click here to reveal e-mail address> wrote in message news:%23%Click here to reveal e-mail address... [Original message clipped] That is true. Thanks. ;) Joe -- Joe Mayo, Author/Instructor Need C#/.NET training? visit www.mayosoftware.com C# Tutorial - www.csharp-station.com Reply to this message...     System.Console System.Int32 System.Object System.ValueType Ad MBR BootFX Best-of-breed application framework for .NET projects, developed by Matthew Baxter-Reynolds and MBR IT

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