C#•2y ago

Init only collection property contructor from IEnumerable

I was wondering if there was a way to assign an IEnumerable to a init only collection property. For example I can do

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" },
};

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" },
};

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" },
};

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" },
};

But I was wondering if I could somehow do

IEnumerable<string> arguments = ...;
ProcessStartInfo psi = new()
{
    ArgumentList = arguments,
};

IEnumerable<string> arguments = ...;
ProcessStartInfo psi = new()
{
    ArgumentList = arguments,
};

IEnumerable<string> arguments = ...;
ProcessStartInfo psi = new()
{
    ArgumentList = arguments,
};

IEnumerable<string> arguments = ...;
ProcessStartInfo psi = new()
{
    ArgumentList = arguments,
};

I'm currently just looping through the enumerable and doing

psi.ArgumentList.Add(a);

psi.ArgumentList.Add(a);

psi.ArgumentList.Add(a);

psi.ArgumentList.Add(a); as a fallback but just wanted to check if there was another way

Keswiik•2/7/24, 11:34 PM

Best you can do in this case would be IEnumerable<string> = new List<string>() { "foo", "bar" }IEnumerable<string> = new List<string>() { "foo", "bar" }

jboreanOP•2/7/24, 11:42 PM

My use case is specifically where the enumerable is through an arg and wanting to set that as the ProcessStartInfo ArgumentList property. From what I can see online it doesn’t seem possible but I thought I would ask in case I’m missing something simple

TheBoxyBear•2/8/24, 1:40 AM

ProcessStartInfo.ArgumentListProcessStartInfo.ArgumentList is a System.Collections.ObjectModel.Collection<string>System.Collections.ObjectModel.Collection<string>, a class with an IList<T>IList<T> constructor so you can simple convert the enumerable to a list and pass it

ProcessStartInfo psi = new()
{
    ArgumentList = new(arguments.ToList()),
}

ProcessStartInfo psi = new()
{
    ArgumentList = new(arguments.ToList()),
}

jboreanOP•2/8/24, 2:19 AM

it's readonly so you can't set it

jboreanOP•2/8/24, 2:19 AM

or at least the only way I can set it is with = { "foo", "bar" },= { "foo", "bar" },

TheBoxyBear•2/8/24, 2:31 AM

Learning something new :dviperHmm: Seems this syntax just calls Add under the hood anyway so looping and adding each item wouldn't be a huge deal in comparison

TheBoxyBear•2/8/24, 2:34 AM

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" }
};

ProcessStartInfo psi = new()
{
    ArgumentList = { "foo", "bar" }
};

would be equivalent to

ProcessStartInfo psi = new();
psi.ArgumentList.Add("foo");
psi.ArgumentList.Add("bar");

ProcessStartInfo psi = new();
psi.ArgumentList.Add("foo");
psi.ArgumentList.Add("bar");

but the collection initializer syntax is only possible during initialization

TheBoxyBear•2/8/24, 2:37 AM

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/object-and-collection-initializers#collection-initializers

Object and Collection Initializers - C# Programming Guide - C#

Object initializers in C# assign values to accessible fields or properties of an object at creation after invoking a constructor.

jboreanOP•2/8/24, 2:47 AM

Makes sense, I'm just sticking with the foreach loop with Add

cap5lut•2/8/24, 8:37 AM

since C# 12 u can use collection expressions

Collection expressions (Collection literals) - C#

Collection expressions are expressions that convert to many different collection types. They enable you to write literal values for collection elements, or import other collection elements into a new collection.

cap5lut•2/8/24, 8:38 AM

eg IEnumerable<string> arguments = ["a", "bc", "def"];IEnumerable<string> arguments = ["a", "bc", "def"];
or IEnumerable<string> arguments = [..someStringCollectionA, "b", ..someOtherStringCollectionC];IEnumerable<string> arguments = [..someStringCollectionA, "b", ..someOtherStringCollectionC];

cap5lut•2/8/24, 8:39 AM

(.... is called spread operator here)

TheBoxyBear•2/8/24, 6:51 PM

The question is about initializing a get-only collection from an IEnumerable. The collection initializer is a workaround that allow adding items to a mutable collection when the reference itself is readonly

jboreanOP•2/9/24, 12:40 AM

https://sharplab.io/#v2:EYLgZgpghgLgrgJwgZwLQGED2AbbEDGMAlpgHYAyRMECU2yAPgAIBMAjALABQTADAARM2AFgDc3PoLYA6ACJEoAc1KZkxfMnFcJAZkEt+6fgG9u/c4L1Nh/ALIAKIToA8Q3gD5+UBIrgBbCFIYZABKEzMLSIAFBEx8FGQAZRhvGABJUjBMfgAHZCJ+AF5+UggAd3sQiMjzUy4ahv4AQR9/QJhKNSL+AG1+aWlvXwCg5H4AXWqagF8tSOnuaaA===
Just to clarify as well, seems like the option won't work. I've fine with the manual looping, just wanted to check if I was missing something

SharpLab

C#/VB/F# compiler playground.

TheBoxyBear•2/12/24, 3:29 PM

Might want to keep an eye on future c# releases. It seems like a small oversight with all the syntax sugar that exists especially regarding collections in recent versions.

TTheBoxyBear Might want to keep an eye on future c# releases. It seems like a small oversight...

cap5lut•2/12/24, 5:01 PM

i totally agree. optimizations for the collection literals will come (iirc some are already merged for .net 9), but generally speaking they provide a way that u would only have to recompile without touching the code at all to get new optimizations in, instead of using some self written code.
(tho there are some uncommon use cases where u cant wait for better performance, but those ppl know what they are doing)

sadly the whole thing doesnt apply here because collection literals require that u can assign a new instance

Init only collection property contructor from IEnumerable

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