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c#.net-8.0collection-initializerc#-12.0

What's the syntax for using C#12 collection expressions to initialise a List<List>>?

Say I have code like this (or any kind of jagged structure):

var intListList = new List<List<int>> {
    new() { 1, 2, 3 }
};

I'd like to use a collection expression here. Resharper (EAP) suggests this:

var intListList = new List<List<int>> {
    [1, 2, 3]
};

But that doesn't compile.

This must be possible! What's the syntax?

Edit:

OK. So from the answers, instead of this, declaring the type in the expression:

// does not compile
var intListList = new List<List<int>> {
    [1, 2, 3]
};

The type has to be declared explicitly, and there is no new():

// compiles!
List<List<int>> intListList = [[1, 2, 3]];
Solution

  • The syntax used for the jagged arrays from the What's new in C# 12:

    // Create a jagged 2D array:
int[][] twoD = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

    Seems to work for lists also:

    List<List<int>> list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

    Online Demo