Practical use of expression trees

c# expression-trees

Question

Expression trees are a nice feature, but what are its practical uses? Can they be used for some sort of code generation or metaprogramming or some such?

Expert Answer

As Jon notes, I use them to provide generic operators with .NET 3.5. I also use them (again in MiscUtil) to provide fast access to non-default constructors (you can't use Delegate.CreateDelegate with constructors, but Expression works fine).

Other uses of manually created expression trees:

But really, Expression is a very versatile way of writing any dynamic code. Much simpler than Reflection.Emit, and for my money, simpler to understand than CodeDOM. And in .NET 4.0, you have even more options available. I show the fundamentals of writing code via Expression on my blog.


Popular Answer

Marc Gravell has used them to great effect in MiscUtil to implement generic operators.




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