Added: LDM notes for July 9th, 2018

[agocke]

https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-07-09.md

Agenda

1. using var feature

   1. Overview
   2. Tuple deconstruction grammar form
   3. using expr; grammar form
   4. Flow control safety

2. Pattern-based Dispose in the using statement

3. Relax Multiline interpolated string syntax ($@)

[svick]

If C# were to allow statements on the top level, a using System; line could either be a using-directive if System is a namespace, or a using-statement if System is a type.

Doesn't C# already allow that, in the scripting mode?

For example, the following code currently runs fine:

using System.Threading.Tasks;
using Microsoft.CodeAnalysis.CSharp.Scripting;

class Program
{
    static async Task Main()
    {
        string code = @"
        using System.IO;
        
        using (Stream.Null);";

        await CSharpScript.EvaluateAsync(code);
    }
}

[gafter]

Regarding flow-control safety:

A new line to the spec should be added saying that, if the end of a using variable's lifetime is reachable, that variable must be definitely assigned at that point.

This needs to also handle constructs like this:

{
    goto label1;
label2:
    return;
    using var x = new FileStream(...);
label1:
    goto label2;
}

The variable x must be definitely assigned at goto label2 because x must be disposed by that control transfer.