Browse questions answered by Jon Skeet

Does Performing a Null Check on a Generic Cause Boxing?

I looked around for this and could not find an answer. Say I have this code: class Command<T> : ICommand<T> { public void Execute(T parameter) { var...

No - at least not in my understanding. If T is a non-nullable value type, the parameter == null check is effectively replaced with false by the JIT compiler; no execution-time check is performed. This is an optimization that only the... more 2/8/2018 12:47:33 PM

Why can't C# infer the type of a DataTable Row

I am trying to iterate over a DataTable and get the values from a particular column. So far I just have the Skeleton of the for loop. foreach (var row in currentTable.Rows) { ...

Why can't C# infer the type of row as it would if I was trying to iterate over a string[] for example? TL;DR: DataTable predates generics :( DataTable.Rows is declared to return DataRowCollection, which derives from... more 2/8/2018 10:08:12 AM

Cannot implicitly convert type void to List

I have below class structure: class Child { public List<ParentData> ParentData { get; set; } } class ParentData { public string FatherName {get;set;} public...

So this part is the problem: GrandParentData=new List<GrandParentData().Add( new GrandParentData { GrandFatherName = "",GrandMotherName =""}); There are three problems here: You're not closing the type argument You've got a... more 2/8/2018 8:08:52 AM

Nodatime Parsing Instant with InstantPattern fails

I use NodaTime, Version=2.2.3.0 I have set up a patter to match various Instant patterns The last pattern should match the examples below. IPattern<Instant> pattern = new...

Firstly, I don't think you actually need that many patterns - I suspect you don't need both M and MM versions, for example. But the problem is that you're using HH with tt. HH means "24-hour clock", so a value of 12 means 12pm... but then... more 2/8/2018 7:44:29 AM

Check IEnumerable using Contains() in a view

I'm trying to render a list of links, and the icon should change depending on wether the item Id is found within an IEnumerable or not. This is the relevant part of my view so...

The problem is that the Contains LINQ method doesn't have the signature you expect - you're trying to check whether an IEnumerable<FrontPageProduct> contains an int... it can't, because it only has FrontPageProduct references. I... more 2/7/2018 9:51:20 AM

Why compilation depends on how exception is thrown within instance initializer?

Why the first code snippet fails to compile (with compile error "Initializer does not complete normally") while the second compiles fine? The only difference is in the way how...

The JLS is pretty clear about this, in section 8.6: It is a compile-time error if an instance initializer cannot complete normally (§14.21). In your first example, the instance initializer can't complete normally. In the second... more 2/6/2018 2:41:32 PM

Hash String does not equal to Copied Hash String from console C#

I created hash. Than I printed it in console. Copied hash value and put it to code for comparsion. But it yield that they are not same. String input = "Hello"; ...

The result of a hash isn't UTF-8-encoded text, and shouldn't be treated that way. Convert it to hex or base64. For example: string computedHashString = Convert.ToBase64String(computedHash); Fundamentally, you need to treat data... more 2/6/2018 2:24:52 PM

Error parsing xml syntax error

I have the following code below. I am getting an error "the character ':' hexadecimal value 0x3A cannot be included in a name" Can anyone tell me how to fix this? Thanks Below is...

Basically, that's not how you handle namespaces in LINQ to XML. You never specify a string with a colon in - instead, you build up an XName from an XNamespace and a string. The good news is that LINQ to XML handling of namespaces is... more 2/2/2018 2:37:15 PM

declare variables in argument list

It's possible in c# 7 to declare variables for out variables in argument list: if (int.TryParse(input, out int result)) WriteLine(result); Is it possible to declare ("non...

You can't do it in the argument list, no. You could use pattern matching for this, but I wouldn't advise it: if (FuncGetStr() is string result && !string.IsNullOrEmpty(result)) That keeps the declaration within the source code... more 2/2/2018 11:57:29 AM

Overloading in local methods and lambda

static void Main() { void TestLocal() => TestLocal("arg"); TestLocal("arg"); } static void TestLocal(string argument) { } In this example, local function has the same...

Why local functions hide methods? Basically it's introducing the method name into the declaration space inside the method. Within that declaration space, the name only refers to the local method... just as it does for a local... more 2/2/2018 9:30:34 AM