C＃Collection Initializer现有集合的语法

Question

There's a syntax in C# that I discovered recently that enables you to initialize a read-only collection during initialization:

class Foo
{
    public List<Bar> Bars { get; } = new List<Bar>();
}

var foo = new Foo
{
    Bars = 
    {
        new Bar()
    }
}

Which is great as it leads to very expressive code. But I have a situation where I already have a collection of Bar , and I want to initialize it using this syntax (even though Bars is readonly ). Is there a way to do this?

var bar = new List<Bar>();
var foo = new Foo
{
    Bars =  bar // error: Property or indexer Foo.Bar cannot be assigned to -- it is read only
}

Answer 1

I want to initialize it using this syntax (even though Bars is readonly)

You simply cannot.

As we are using the initializer syntax and it actually call the setter method aka set of the property and you have a readonly property which can only be set by the class itself and for setting it form outside the class we need to pass it via constructor of Foo while creating it's instance.

UPDATE:

The first example code actually ends up call to Add method of the List<T> . It will compiled to following code:

 Foo foo = new Foo();
 foo.Bars.Add(new Bar());

While you can add new items to the Bars but you cannot change it's reference to point to a different object directly using the initializer due to read-only property while it's totally legit to call the member method of List<Bar> on the instance like Remove , Find etc.