CODEWITHSUNDEEP
c#
Alex Butenko
Alex Butenko

Reputation: 3774

Weird syntax of collection initializers

Suppose, we have a very simple class:

class ObjectList {
    public List<string> List1 { get; } = new List<string>();
    public List<string> List2 { get; set; }
}

and we want to make an instance of this class:

ObjectList objectList = new ObjectList {
    List1 = { "asdf", "qwer" },
    List2 = new List<string> { "zxcv", "1234" }
};

So, in case of List2 it is ok, using "=" we set property. But in List1 case it looks like we set property, but actually, we suppose to set it somewhere before, and here we only set values. And it very similar to array initializing:

string[] arr = { "val1", "val2" }

Why C# uses this confusing syntax here?

Edit: I guess I confused many viewers with C# 6.0 syntax, but it's not the point. Let's use old good C# 3.0 and .net 2.0. And lets add more fun too this and add some values ("1" and "2") to the list from start, as Jeff Mercado recommended:

class Program {
    static void Main(string[] args) {
        ObjectList objectList = new ObjectList {
            List1 = { "asdf", "qwer" },
        };
    }
}
class ObjectList {
    List<string> _List1 = new List<string>() { "1", "2" };
    public List<string> List1 {
        get {
            return _List1;
        }
    }
}

It shows the same weird syntax. And at the end I have list { "1", "2", "asdf", "qwer" }, which is even more confusing. I can expect this the less.

Upvotes: 5

Views: 185

Answers (2)

Carlos Mu&#241;oz
Carlos Mu&#241;oz

Reputation: 17844

The answer has been given by Eric Lippert in his answer to Why is an Add method required for { } initialization?

The by-design goal motivated by typical usage scenarios for collection initializers was to make initialization of existing collection types possible in an expression syntax so that collection initializers could be embedded in query comprehensions or converted to expression trees.

Every other scenario was lower priority; the feature exists at all because it helps make LINQ work.

So it seems that, even when this syntax makes more sense when creating readonly collections, it was added anyway so they can deliver LINQ on time.

Upvotes: 2

Henk Holterman
Henk Holterman

Reputation: 273804

Why C# uses this confusing syntax here?

You are right that it's a little bit weird, but that's because you are mixing 2 principles. As several comments already pointed out, the { item1, items2 } syntax is converted to .Add(itemN) calls when the item on the left of the = is a Collection.

So the weirdness is a result of the fact that 

List<SomeClass> list = new List<SomeClass> { item1, item2 };
SomeClass[] array = { item1, item2 };

are treated differently.

The other part is that your sample moves the new List<SomeClass> around, but it is there in both cases.

Upvotes: 3

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