Question

I have been curious about dynamically create class at runtime in C# and stumbled across this article. http://olondono.blogspot.com/2008/02/creating-code-at-runtime.html I am curious to hear some pros and cons regarding construction of a class at runtime.

Any opinions?

Answer 1

Meta-programming has all the advantages of build-time code-gneneration, but without the additional code step. This is very common in library code, such as ORMs, serializers, some types of AOP, DI/IoC containers, etc.

• + avoids the need for extra build steps or writing mundane code
• + such code can handle what actually is the case at runtime, rather than having to handle any uncommon edge-cases or lots of wrappers around wrappers (decorator pattern)
• + allows codegen in scenarios where the metadata is only known at runtime
• + runtime IL can have more access to private fields etc, thanks to how DynamicMethod can be associated with a type; fully generated (dll) code would require [InternalsVisibleTo] or similar, which may be impossible
• – not all systems support runtime code-gen; it is disabled on some server setups, compact framework, iPhone, etc
• – it is bug ugly to do. Regardless of how you do it, this is not normal code.
• – it needs a really good understanding of how things actually work under the covers
• + if forces you to get a really good understanding of how things actually work under the covers

I’m currently re-writing an existing library to use runtime IL generation; it is very rewarding and I’m happy with it; but it is unlike anything I’ve written before.