Web Log di Adrian Florea

"You know you've achieved perfection in design, not when you have nothing more to add, but when you have nothing more to take away." Antoine de Saint-Exupery
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gennaio 2009 Blog Posts

Sul cast del foreach

Nel suo post di ieri, "foreach l'insidioso", Luca si e' chiesto come mai il seguente snippet: using System.Collections.Generic; interface IPersistent { } class Invoice : IPersistent { } class Order : IPersistent { } class Program {     static void Main() {         List<IPersistent> changedDocuments = new List<IPersistent>();         changedDocuments.Add(new Invoice());         changedDocuments.Add(new Order());         foreach (Invoice changedInvoice in changedDocuments) { }     } } compili. Secondo me, il comportamento del compilatore e' giusto, voluto e documentato. Le specifiche del linguaggio (15.8.4, ECMA-334), dicono: "A foreach statement of the form foreach(V v in x) embedded-statement is then expanded to: {     E e = ((C)(x)).GetEnumerator();     try {         V v;         while (e.MoveNext()) {             v = (V)(T)e.Current;             embedded-statement         }     }     finally {         … // Dispose e     } } The variable e is not visible to or accessible to the...

posted @ mercoledì 14 gennaio 2009 11:11 | Feedback (96) | Filed Under [ Carillon .NET ]

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