Champion "Expression variables in initializers" (15.7) about csharplang HOT 5 OPEN

The following code is now legal in query clauses.

var strings = new string[1];

var r = from s in strings
        select int.TryParse(s, out var i); 

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Handing off to @AlekseyTs to drive the LDM discussion.

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I'm struggling to find documentation about exactly what this change entails, as the links seems to go around in a circle and end up on this page that seems to tell me that nothing has been implemented, yet it is listed in the Visual Studio 15.3 release notes as released.

Can anyone shed some light on this, or is it perhaps obvious to everyone but me what this change is about?

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See dotnet/roslyn#16270.

With C# 7.3 in VS2017 v15.7 (thought not the .NET Core CLI tools or Visual Studio for Mac yet), the following code is now legal. Previously, they would trigger the compiler error CS8200.

using System.Collections.Generic;
using System.Linq;

public class A
{
    public A(int i)
    {
    }
    
    public static int Magic = int.TryParse("123", out var i) ? i : 0;
}

public class B : A
{
    public B(string s)
        : base(int.TryParse(s, out var i) ? i : 0)
    {
    }
}

This covers both constzuctor-initializers and field-initialisers. I'm not sure about query clauses, I haven't been able to find an example that used to cause a compiler error but now works.

FWIW, the 2.7.0 compilers in SharpLab don't like the above just yet, but the master branch does.

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It seems that returns IEnumerable<bool>.

Will this work too? I.e., referring to the expression's variable?

var r = from s in strings
        select int.TryParse(s, out var i) ? i : (int?)null;

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