null-coalescing-operator

take a look at the following code I attempted to write inside a constructor: private Predicate<string> _isValid; //... Predicate<string> isValid = //...; this._isValid = isValid ?? s => true; The code doesn't compile - just "invalid expression term"s and so one. In contrast that does compile and I could just use it: this._isValid = isValid ?? new Predicate<string>(s => true); However, I still wonder why this syntax is not allowed. Any ideas? this._isValid = isValid ?? (s => true); Will work :) It parsed it this way: this._isValid = (isValid ?? s) => true; which does not make any sense. Check

If I have code similar to the following: while(myDataReader.Read()) { myObject.intVal = Convert.ToInt32(myDataReader["mycolumn"] ?? 0); } It throws the error: Object cannot be cast from DBNull to other types. defining intVal as a nullable int is not an option. Is there a way for me to do the above? Can you use an extension method? (written off the top of my head) public static class DataReaderExtensions { public static T Read<T>(this SqlDataReader reader, string column, T defaultValue = default(T)) { var value = reader[column]; return (T)((DBNull.Value.Equals(value)) ? defaultValue : Convert

Possible Duplicates: Coalesce operator and Conditional operator in VB.NET Is there a VB.NET equivalent for C#'s ?? operator? Is there a built-in VB.NET equivalent to the C# null coalescing operator? Cody Gray Yes, there is, a long as you're using VB 9 or later (included with Visual Studio 2008). You can use the version of the If operator overloaded to accept only two arguments: Dim myVar? As Integer = Nothing Console.WriteLine(If(myVar, 7)) More information can be found here in a blog post by the VB.NET team. (Yes, this is an operator , even though it looks like a function. It will compile

When interacting with C# libraries, I find myself wanting C#'s null coalescing operator both for Nullable structs and reference types. Is it possible to approximate this in F# with a single overloaded operator that inlines the appropriate if case? Yes, using some minor hackery found in this SO answer " Overload operator in F# ". At compiled time the correct overload for an usage of either ('a Nullable, 'a) ->'a or ('a when 'a:null, 'a) -> 'a for a single operator can be inlined. Even ('a option, 'a) -> 'a can be thrown in for more flexibility. To provide closer behavior to c# operator, I've

null coalescing translates roughly to return x, unless it is null, in which case return y I often need return null if x is null, otherwise return x.y I can use return x == null ? null : x.y; Not bad, but that null in the middle always bothers me -- it seems superfluous. I'd prefer something like return x :: x.y; , where what follows the :: is evaluated only if what precedes it is not null . I see this as almost an opposite to null coalescence, kind of mixed in with a terse, inline null-check, but I'm [ almost ] certain that there is no such operator in C#. Are there other languages that have