Question

what I want to do is really basic, I think. To code example shows it clearly.

class MyClass{
     public string[] Bar;
}

MyClass Foo = new MyClass();
Foo.Bar = { "word", "word", "word" };

This code gives me an error in Visual Studio C#. (Only assignment, call, increment, decrement, and new object expressions can be used as a statement)

Is there a better way to provide an array to the class? The array could be const for my part.

How can I provide an (const) array to a class from outside?

I don’t want to use the constructor, because the array should be optionally.

Answer 1

You can only initialize arrays using the {} without the new operator as part of a declaration (which in turn has to explicitly specify the array type). This has nothing to do with whether it’s in the same class or not:

int[] x = { 1, 2, 3 }; // Fine
x = { 4, 5, 6 }; // Fail
x = new[] { 7, 8, 9 }; // Implicitly typed array as of C# 3
x = new int[] { 10, 11, 12 }; // Works with all versions of C#

See sections 12.6 (array initializers), 10.5 (field declarations), 8.5.1 (local variable declarations) and 7.6.10.4 (array creation expressions) of the C# 4 specification for details.

To answer your comment on Darin’s post: no, there’s no such thing as a “const” array in any sense I can imagine you mean. Even if you make the array variable readonly, like this:

private static readonly int[] Values = { 1, 2, 3 };

that only makes the variable read-only. Values will always refer to the same array object (which will therefore always have 3 elements) but arrays themselves are always mutable. If you want to build a read-only collection, I’d suggest using ReadOnlyCollection<T>, probably via List.AsReadOnly():

private static readonly ReadOnlyCollection<int> Values =
    new List<int> { 1, 2, 3 }.AsReadOnly();