Using Statement

using statement is a missing part of LINQ Expressions. Metaprogramming library provides such support.

using DotNext.Linq.Expressions;
using System;
using System.IO;
using static DotNext.Metaprogramming.CodeGenerator;

Lambda<Action<byte[]>>(fun => 
{
    Using(typeof(MemoryStream).New(fun[0]), stream => 
    {
        Call(stream, nameof(MemoryStream.Flush));
    });
});

//the generated code is
new Action<byte>(bytes =>
{
    using (var s = new MemoryStream(bytes))
    {
        s.Flush();
    }
});

stream parameter represents disposable resource inside of Using() scope.

Using statement can accept any expression of type implementing System.IDisposable interface or having public instance method Dispose() without parameters.

Async Disposable

await using statement in C# allows to control the lifetime of the resource implementing IAsyncDisposable interface. The same statement is supported by Metaprogramming library:

using System.IO;
using System.Threading.Tasks;
using static DotNext.Metaprogramming.CodeGenerator;

AsyncLambda<Func<byte[], Task>>(fun => 
{
    AwaitUsing(typeof(MemoryStream).New(fun[0]), stream => 
    {
        Call(stream, nameof(MemoryStream.Flush));
    });
});

//the generated code is
new Func<byte[], Task>(async bytes => 
{
  await using (var s = new MemoryStream(bytes))
  {
      s.Flush();
  }
});

This type of statement is allowed within async lambda expression only.