Is there a {} Operator?

Question

You can use

List<string> sList = new List<string>() { "1", "2" };

to create a new List and add 2 items. The { "1", "2" }-part only works because List<T> has implemented a Add() method.

my question: is {} something like a operator and can it be overloaded e.g. to add items twice

its not an operator. here is the list of operators https://msdn.microsoft.com/en-us/library/6a71f45d.aspx — M.kazem Akhgary, Sep 24 '15 at 12:24
@JonSkeet the result would be `1,1,2,2` - but that's just a example. i want to know if i can get between the `{}` and the `Add()` — Byyo, Sep 24 '15 at 12:27
And the answer is "no, but you can provide your own Add method" - depending on the class involved, of course. — Jon Skeet, Sep 24 '15 at 12:35

score 12 · Accepted Answer · edited May 23 '17 at 12:29

12

is {} something like a operator and can it be overloaded e.g. to add items twice

Any collection type which provides an Add method, built in or as an extension method (starting from C#-6), can use the collection initializer provided by the { } syntax. If your Add method adds the same item twice to that collection, then that is what it will do.

If you'd want the behavior of { } to change, you'd have to override or overload the Add method on the collection.

Some additional specification goodness (taken from this answer):

C# Language Specification - 7.5.10.3 Collection Initializers

The collection object to which a collection initializer is applied must be of a type that implements System.Collections.IEnumerable or a compile-time error occurs. For each specified element in order, the collection initializer invokes an Add method on the target object with the expression list of the element initializer as argument list, applying normal overload resolution for each invocation. Thus, the collection object must contain an applicable Add method for each element initializer.

edited May 23 '17 at 12:29

Community

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answered Sep 24 '15 at 12:25

Yuval Itzchakov

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Or overload it. Or (as of C# 6) add an extension method. – Jon Skeet Sep 24 '15 at 12:26
@JonSkeet As of C#6, does it still need to implement `IEnumerable`? I only ask because [this](https://msdn.microsoft.com/en-us/library/bb384062.aspx) says "*...when you initialize a collection class that implements IEnumerable or a class with an Add extension method*" – Rawling Sep 24 '15 at 12:28
Adding a `Add` method has been available for a while as an extension method, hasn't it been? – Yuval Itzchakov Sep 24 '15 at 12:29
@Rawling: Yes, it does. That's a documentation bug :( – Jon Skeet Sep 24 '15 at 12:34
@YuvalItzchakov: Add extension methods weren't usable *for colleciton initializers* before C# 6, AFAIK... – Jon Skeet Sep 24 '15 at 12:34
@JonSkeet Right, just looked that up. It was VB.NET that had it for a while. – Yuval Itzchakov Sep 24 '15 at 12:38
@JonSkeet Fair enough. I hoped they'd dropped it, I never liked that restriction. – Rawling Sep 24 '15 at 12:40

Is there a {} Operator?

1 Answers1

C# Language Specification - 7.5.10.3 Collection Initializers