[ComputerGuru]

The usual C# reflection APIs that devs turn to allocate a lot, but there are ways to make them almost performant by (re)using delegates and expressions. There are a number of good libraries to use reflection faster, as well.

[int_19h]

IIRC, dynamically compiled expression trees in C# have the overhead of a single virtual call (on the resulting delegate) when executing - and cover all object factory and member access scenarios. But if you need to discover metadata, you still have to resort to Reflection APIs.

[kevingadd]

The main corner case that still causes me problems is that if you want to construct a delegate at runtime, this often forces you to go through the reflection APIs to actually grab the method even if you know its full signature, etc. My current project has a JIT compiler for scripts that has this problem (I ended up finding a workaround involving getting LINQ to generate method tokens in an assembly, but .NET Core / .NET 5 deprecated LINQ compilation...)