Tag: Assembly Loading

Categories
Computers and Internet

Referencing a .NET assembly in a compile time safe manner

If you need to provide a System.Reflection.Assembly instance to an API [1], there are several mechanisms for doing so. They roughly split into two camps:

  • Run-time assembly loading
  • Assemblies known at compile time

The run-time assembly loading includes scenarios such as having a plug-in architecture where the code being referenced cannot be known at the time of compilation.

For the other camp, if we know exactly which assembly we need to reference at compile time we have a couple of options. We can use the name of the assembly as a string like so:

Assembly.Load(“MyCompany.Util”);

(Note that if the assembly is already loaded the runtime will just return the loaded instance of that assembly and won’t attempt to load it again.)

Alternatively we can use a type from that assembly like so:

Assembly.GetAssembly(typeof(MyCompany.Util.AnyOldClass);

The problem with the assembly name string approach is that there is no compile time checking. The typeof approach allows for compile time checking but introduces an artificial dependency in the calling code on a class that it only needs for the purposes of getting the assembly. This calling code is then subject to any renaming or removal of that class when in reality it cares only about the assembly and not the type.

The solution I’ve gone for is to create a static, empty class with a similar name to the assembly in the root of the default namespace of the assembly I wish to reference and use this in the typeof:

using MyCompany.Util;
/* … */
Assembly.GetAssembly(typeof(MyCompanyUtil));

This provides us with a compiler error if the assembly reference is dropped or the assembly is renamed. It will take part in any necessary refactoring operations and is not dependent on irrelevant types.

 

[1] Examples include Autofac’s MVC and WebApi integration: ContainerBuilder.RegisterControllers & ContainerBuilder.RegisterApiControllers

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