2.4 Assemblies & DLL basics

This completes the Namespaces & Code Organization section by showing how code is packaged and distributed.

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📌 1. What Is an Assembly?

• An assembly is the compiled output of C# code — usually a .exe or .dll file.

• It is the building block of .NET applications.

• Contains:

  1. IL code (Intermediate Language) — the compiled C# code.

  2. Metadata — info about types, members, references.

  3. Manifest — info about version, culture, dependencies.

• DLL (Dynamic Link Library) = library assembly (no standalone execution).

• EXE = executable assembly (can run directly).

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📌 2. How Namespaces Relate to Assemblies

• Namespaces group types logically in code.

• Assemblies group compiled code physically.

• One assembly can contain multiple namespaces, and one namespace can span multiple assemblies.

Assembly: MyApplication.dll
 ├─ Namespace: MyApplication
 │    ├─ Class Program
 │    └─ Class Helper
 ├─ Namespace: MyApplication.Models
 │    └─ Class User

• When you reference a DLL, you gain access to all namespaces and types inside that assembly.

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📌 3. Referencing Assemblies

1. Via Visual Studio

• Right-click References → Add Reference → Browse / Projects / NuGet

• Once added, you can using NamespaceName; to access its types.

2. Via .NET CLI

dotnet add reference ../MyLibrary/MyLibrary.csproj

• Then in code:

using MyLibrary.Utilities;

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📌 4. Benefits of Assemblies

1. Code reuse — share compiled libraries across multiple projects.

2. Versioning — different assemblies can have version info.

3. Encapsulation — hide internal implementation; only public types are accessible.

4. Modularity — large projects can be split into multiple DLLs.

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📌 5. Key Points

Feature	Notes
Assembly	Compiled unit (.exe or .dll)
Manifest	Metadata + version info
DLL	Library assembly (cannot run standalone)
Namespace	Logical grouping of types (may span assemblies)
Reference	How a project gains access to another assembly
NuGet	Package manager to distribute assemblies easily

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📌 6. Analogy

• Namespace = folder with related files

• Assembly = ZIP archive containing folders (namespaces)

• DLL = library ZIP (cannot run alone)

• EXE = runnable ZIP (application)

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✅ Summary:

• Assemblies are physical compiled units in .NET.

• Namespaces are logical groupings of types inside assemblies.

• Understanding assemblies is key for code reuse, modularity, and referencing external libraries.

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Next, if you like, we can create a complete “Namespaces & Code Organization” mini-section for your guide, combining:

• namespace

• using / global using

• extern alias

• Assemblies & DLLs