疑问：未知使用语言的DLL为何能返回C# DBConnection类对象

Great question—this gets right to how .NET's cross-language compatibility works under the hood! Let's break this down simply:

First, that DLL is almost certainly a .NET managed assembly (written in C#, VB.NET, or another .NET language). It's not returning a "C#-exclusive" object—it's returning a CLR (Common Language Runtime) type instance that all .NET languages can understand.

Here's the key breakdown:

• .NET's Unified Type System: Every .NET language compiles down to Intermediate Language (IL) and runs on the CLR. The CLR uses a shared type system, so a DBConnection (whether it's your custom class or the built-in System.Data.Common.DbConnection) defined in a C# DLL is a CLR type, not a "C# type". When you call this DLL from C#, VB.NET, F#, or any other .NET language, the runtime recognizes that type natively.
• The DLL Doesn't Care About the Calling Language: The DLL only needs to expose types that follow CLR rules. As long as the calling code is running in a .NET environment, it can interact with those types seamlessly. Think of it like a PDF file—it doesn't matter if you open it with Adobe Reader, Chrome, or Edge; the format is universal to tools that understand it.
• Non-Managed DLLs Can't Do This: If this were a native (unmanaged) DLL (written in C/C++, for example), it could never directly return a C# DBConnection object. You'd have to use P/Invoke to bridge the gap, and the return value would be something like a pointer or primitive data type—not a fully managed .NET object. Your scenario clearly involves a managed DLL, since you're getting a complete DBConnection instance directly.

One last way to wrap your head around it: When you see a "C# object" being returned, you're just seeing a CLR object that C# is presenting using its own syntax. A VB.NET developer calling the same DLL would see the exact same object—they'd just declare it with VB syntax like Dim conn As DBConnection instead of C#'s DBConnection conn.

内容的提问来源于stack exchange，提问作者Guilherme Albertini