Question

I read about the Conditional attribute today. According to MSDN:

Applying ConditionalAttribute to a method indicates to compilers that a call to the method should not be compiled into Microsoft intermediate language (MSIL) unless the conditional compilation symbol that is associated with ConditionalAttribute is defined.

OK. That’s clear. So the call to the method will not be compiled. But what about side effects?

[Conditional('UndefinedCondition')] static void f1(int x) { Console.WriteLine(x); }  static int a = 0; static void f2() { f1(++a); } 

So when f2 is called, the call to f1 should be removed. But why is ++a removed as well? This does’t make any sense to me!

Answer 1

Expanding on Marc’s answer.

This is definitely ‘By Design’. The best way to understand the rationalization for this is to think about what this code took the place of. This feature in many, and much cleaner ways, takes the way of conditionally compiled code.

For example,

#if DEBUG f1(++a); #endif 

Or another version

#define f1(x) ... 

In the non-debug case there are clearly no side effects. This is same behavior for [Conditional] code. I agree it’s definitely not as clear as the first example, but it is as clear as the second one.