What are the advantages and disadvantages of using the GAC?

Question

And on top of that, are there cases where one has to use the global assembly cache or where one cannot use it?

Answer 1

If you're shipping a reusable library consisting of multiple assemblies, but only few of them form a facade, you can consider installing the assemblies into GAC, if the package is installed to developer's PCs.

Imagine, you ship 6 assemblies, and only one of these 6 assemblies contains a facade - i.e. other 5 are used only by the facade itself. You ship:

• MyProduct.Facade.dll - that's the only component intended to be used by developers
• MyProduct.Core.dll - used by MyProduct.Facade.dll, but not intended to be used by developers
• MyProduct.Component1.dll - the same
• MyProduct.Component2.dll - the same
• ThirdParty.Lib1.dll - third-party library used by MyProduct.Component1.dll
• ThirdParty.Lib2.dll - the same
• etc.

Developers using your project would like to reference just MyProduct.Facade.dll in their own projects. But when their project runs, it must be able to load all the assemblies it references - recursively. How this can be achieved? In general, they must be available either in Bin folder, on in GAC:

• You may ask the developers to locate your installation folder and add references to all N assemblies you put there. This will ensure they'll be copied into Bin folder to be available in runtime.
• You may install VS.NET project template already containing these 6 references. A bit complex, since you should inject the actual path to your assemblies into this template before its installation. This can be done only by installer, since this path depends on installation path.
• You may ask developers to create a special post-build step in .csproj / .vbproj file copying the necessary dependencies to Bin folder. The same disadvantages.
• Finally, you may install all your assemblies into GAC. In this case developers must add the reference just to MyProduct.Facade.dll from their project. Everything else will be available in runtime anyway.

Note: last option doesn't make you to do the same while shipping the project to production PCs. You can either ship all the assemblies within Bin folder, or install them into GAC - all depends all your wish.

So the solution described shows the advantage of putting third-party assemblies into GAC during the development. It doesn't related to production.

As you may find, installation into GAC is mainly intended to solve the problem of location of required assemblies (dependencies). If an assembly is installed into GAC, you may consider it exists "nearby" any application. It's like adding path to .exe to your PATH variable, but in "managed way". - of course, this is rather simplified description ;)