Creating an list ...

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I have a beginner question.
I'm used to seeing a list created with the following syntax:

List<Employee> emp = new List<Employee>();

but I recently saw an List defined like this:

List<Employee><employee> emp = new List<Employee><employee>

What is the purpose of the second pair of angled brackets?

Thanks,
C. T.

What I have tried:

What I specified above ... simple question about C# functionality

Posted 23-Mar-19 8:40am

Charles T. Blankenship

Updated 23-Mar-19 10:32am

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Comments

Maciej Los 23-Mar-19 15:00pm

Are you sure that second brackets aren't circle brackets?

Charles T. Blankenship 23-Mar-19 15:09pm

Yes sir ... positive ... I got it from an article here on CodeProject ... here is the link:

https://www.codeproject.com/Articles/897559/Learn-MVC-in-days-Day

Charles T. Blankenship 23-Mar-19 15:16pm

I'm pretty sure it is invalid C# syntax ... but just wanted to make sure C# didn't introduce something I didn't know about.

2 solutions

Solution 2

A List<T> Class (System.Collections.Generic) | Microsoft Docs[^] does not have such of constructor[^].

There's only one constructor which accepts circle brackets: List<T>(IEnumerable<T>). See:

C#

void Main()
{
	
	
	string[] dinos = {"Tyrannosaurus",
	        "Amargasaurus",
	        "Mamenchisaurus",
	        "Deinonychus",
	        "Compsognathus"};
	
	List<Dinosaur> dinosaurs = new List<Dinosaur>(dinos.Select(x=>new Dinosaur(){Name=x}));
	//dinosaurs list has been initiated and set
	
			
}

// Define other methods and classes here
public class Dinosaur
{
	public string Name = string.Empty;

}

So, it's a bug in referenced article.

Posted 23-Mar-19 10:32am

Maciej Los

Comments

BillWoodruff 24-Mar-19 5:29am

+5 Hi, call me a fanatic: I always insist my students use new[] :)

This will work too:

List<dinosaur> dinolist = dinos.Select(dino => new Dinosaur() { Name = dino }).ToList();

Maciej Los 24-Mar-19 5:44am

Hi, Fanatic ;)
Thank you very much, Bill.
Cheers
Maciej

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phil.o · Accepted Answer · 2019-03-23T10:06:00

It is indeed invalid syntax. What happened is that the author of the article did not escape brackets while writing its code-block; the system considered they were unclosed tags and tried to "correct" the mistake, leading to an incorrect syntax. Obviously the author did not notice the fact. By reading the comments to the article, you will find that several users have reported the issue.