<div>
This is total speculation, but the <b>async</b> and <b>await</b> keywords are just syntactic sugar for the compiler to create a state machine for you. Since <b>async</b> methods return <b>Task&lt;T&gt;</b>, and <b>Task</b> was introduced in .NET 4.0, it may be possible. It could be worth putting together a quick throw-away project to test.
</div>


This is total speculation, but the async and await keywords are just syntactic sugar for the compiler to create a state machine for you. Since async methods return Task<T>, and Task was introduced in .NET 4.0, it may be possible. It could be worth putting together a quick throw-away project to test.

<div>
I'm thinking that the machine running the consuming program would implement the DLL alright, even if that program was a 4.0 framework program, so long as the 4.5 framework was installed on that machine.<br />
<br />
Sorry for the delay in responding guys.
</div>


I'm thinking that the machine running the consuming program would implement the DLL alright, even if that program was a 4.0 framework program, so long as the 4.5 framework was installed on that machine.

Sorry for the delay in responding guys.

<div>
<div class="content wysiwyg-content">
I am building a DLL for my office and it needs to use Async (a 4.5 framework tool). &nbsp;Many of our programs that use this DLL are 4.0 framework apps. &nbsp;So can I put async in the DLL and still have those programs use the methods that have async in them (BTW, no 4.5 objects will be returned to the calling program)?
</div>
</div>


I am building a DLL for my office and it needs to use Async (a 4.5 framework tool).  Many of our programs that use this DLL are 4.0 framework apps.  So can I put async in the DLL and still have those programs use the methods that have async in them (BTW, no 4.5 objects will be returned to the calling program)?

Can a VS 4.0 framework app consume a VS 4.5 framework DLL?

The .NET Framework is not specific to any one programming language; rather, it includes a library of functions that allows developers to rapidly build applications. Several supported languages include C#, VB.NET, C++ or ASP.NET.

.NET Programming

Visual Basic .NET (VB.NET) is an object-oriented programming language implemented on the .NET framework, but also supported on other platforms such as Mono and Silverlight. Microsoft launched VB.NET as the successor to the Visual Basic language. Though it is similar in syntax to  Visual Basic pre-2002, it is not the same technology,

Visual Basic.NET

C# is an object-oriented programming language created in conjunction with Microsoft’s .NET framework. Compilation is usually done into the Microsoft Intermediate Language (MSIL), which is then JIT-compiled to native code (and cached) during execution in the Common Language Runtime (CLR).