Conditional compilation based on constants?

Question

Is it possible to conditionally compile classes and methods based on some constant value defined in a class, for example I\'d like to have something like that.

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Answer 1

No -

C# does not evaluate expressions in the #if preprocessor directive - it only looks to see if the symbol is defined :

When the C# compiler encounters an #if directive, followed eventually by an #endif directive, it compiles the code between the directives only if the specified symbol is defined. Unlike C and C++, you cannot assign a numeric value to a symbol. The #if statement in C# is Boolean and only tests whether the symbol has been defined or not.

(emphasis added)

So the proper way to do what you want is to do:

public class SomeClass {
   #if BUILD_MODE_ONE
       public void SomeMethod() { /* Implementation one */ }
   #elif BUILD_MODE_TWO
       public void SomeMethod() { /* Implementation two */ }
   #elif BUILD_MODE_THREE
       public void SomeMethod() { /* Implementation three */ }
   #endif
}

Where the symbol could either be defined in that code file or via command-line parameters to CSC.EXE.