Why is a cast needed here?

[Dave]

import std.socket;

void main()
{
//Socket s = new Socket(AddressFamily.INET,SocketType.STREAM,ProtocolType.TCP);
   Socket s = new Socket(cast(AddressFamily)AddressFamily.INET,SocketType.STREAM,ProtocolType.TCP);
}

Why is the 'cast(AddressFamily)' needed?

W/o the cast:

t.d(5): constructor std.socket.Socket.this () does not match parameter types 
(int,SocketType,ProtocolType)
t.d(5): Error: cannot implicitly convert expression (2) of type int to AddressFamily
t.d(5): Error: cannot implicitly convert expression (6) of type ProtocolType to char[]
t.d(5): Error: cannot cast int to char[]

Thanks!