Passing zero (int) to an enum in .NET Socket constructor?!

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Guest

This code compiles (this is how it should work):
Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream,
ProtocolType.Tcp);

This code does not compile (passing an int instead of an AddressFamily is
bad):
Socket sock = new Socket(1, SocketType.Stream, ProtocolType.Tcp);

But why on earth does not compile:
Socket sock = new Socket(0, SocketType.Stream, ProtocolType.Tcp);

Is the number zero some kind of special case here? Why is zero accepted when
the parameter type clearly says that an AddressFamily enum value is expected?!


regards,
martin
 
martin said:
This code compiles (this is how it should work):
Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream,
ProtocolType.Tcp);

This code does not compile (passing an int instead of an AddressFamily is
bad):
Socket sock = new Socket(1, SocketType.Stream, ProtocolType.Tcp);

But why on earth does not compile:
Click to expand...

Typo, I assume.
Socket sock = new Socket(0, SocketType.Stream, ProtocolType.Tcp);

Is the number zero some kind of special case here? Why is zero accepted when
the parameter type clearly says that an AddressFamily enum value is expected?!
Click to expand...

Yes, zero is a special case. Here is a shorter example:

System.Net.Sockets.AddressFamily af1 = 1; // no compile
System.Net.Sockets.AddressFamily af1 = 0; // compile

The reason can be found in section 6.1.3 of the C# spec:

<http://msdn.microsoft.com/library/d...y/en-us/csspec/html/vclrfcsharpspec_6_1_2.asp>

(sic, the url says 6.1.2 but the page is 6.1.3 :))
C# Language Specification

6.1.3 Implicit enumeration conversions
An implicit enumeration conversion permits the decimal-integer-literal
0 to be converted to any enum-type.
Elsewhere in the docs, we are also told "The default value of an enum E
is the value produced by the expression (E)0."
 
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