Instantiate a List inside of type initializer

Question

Say I have a struct like so

public struct MyStruct { string StructConfig { get; set; } List<string> Details { get; set; } public MyStruct { Details = new List<string>(); } }

And I instantiate this struct using:

MyStruct s = new MyStruct() { StructConfig = "Some config details" }

I'm wondering how I could add a foreach loop that will add the details into the Details property, rather than doing:

MyStruct s = new MyStruct() { StructConfig = "Some config details" } s.Details = new List<string>(); foreach (var detail in someArray) s.Details.Add(detail);

Is this even possible? Am I dreaming of code-luxury?

Sergey Kalinichenko · Accepted Answer · 2012-03-29 12:42:45Z

You can do it like this:

MyStruct s = new MyStruct() { StructConfig = "Some config details", Details = new List<string>(someArray) }

This works because List<T> supports initialization from IEnumerable<T> through this constructor.

If you need to do additional preparations on the elements of someArray, you could use LINQ and add a Select. The example below adds single quotes around each element:

Details = new List<string>(someArray.Select(s => string.Format("'{0}'", s)))

I think you need to remove the ; as that will give an excpetion.

leppie · Accepted Answer · 2012-03-29 11:18:21Z

1

How about?

s.Details = new List<string>(someArray);

answered Mar 29, 2012 at 11:18

leppie

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Comments

Martin Liversage · Accepted Answer · 2012-03-29 11:20:23Z

Assuming that you don't want to initialize the list from an array but really want to be able to write the list elements directly in your initializer you can use a collection initializer:

var myStruct = new MyStruct() { StructConfig = "Some config details", Details = new List<string>() { "a", "b", "c" } };

^{Now, having a struct containing a string and a list of strings looks slightly weird but that doesn't affect how to answer the question.}

trembon · Accepted Answer · 2012-03-29 11:20:14Z

can do something like this

MyStruct s = new MyStruct { StructConfig = "Some config details", Details = someArray.ToList() };

Andy Holt · Accepted Answer · 2012-03-29 11:20:38Z

You could call the extension method ToList() on the "someArray" collection, which will create a copy of it that you could assign to your struct property, like so:

MyStruct s = new MyStruct() { StructConfig = "Some config details", Details = someArray.ToList() }

Jason · Accepted Answer · 2012-03-29 11:23:37Z

Something along the lines of:

s.Details = someArray.Select(detail=> detail.ToString()).ToList()

Would prevent an exception being thrown were your array not a string[]. Of course, you may wish for the exception to be thrown in this case.

Also, it's worth considering why you are using a struct with a property that is a List; it may be better to have a class instead of a struct.

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