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Comment by ridiculous_fish | Hacker News Reader

> D has no need for a preprocessor

How does this work, specifically conditional compilation? I have lots of code like this:

   #if __APPLE__
      /* do things the OS X way */
   #else
     /* do things the Linux way */
   #endif

Where the OS X way calls functions that do not exist on Linux, and vice-versa. How does D handle this?

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Check out https://github.com/D-Programming-Language/phobos/blob/master... at line 33 and on. You'll see: version (Windows) { ... } etc. For the specification on how this works:

http://dlang.org/version.html

The salient point is that conditional compilation in D is not text based, it is AST based. Furthermore, for 'static if', the conditional expression has access to the full symbol table and power of the D language - it is not a separate preprocessor language with its own rules and separate symbol table.

Thank you for the reply. That's very elegant!

Can it do more complex ifdefs - with or's and and's etc?

'static if' can - it has full access to the language.

    version (Posix) {
      version(OSX) {
        // Weird stuff on OSX
      }
    // Sane stuff for Linux or FreeBSD
    }
    version (Windows) {
      // Weird stuff for Windows
    }

But think that this is processed by the compiler, not by a text pre-processor. Also, you can use your own version stuff, for example here : https://github.com/Zardoz89/nBodySim/blob/master/source/app.... there is a "PFor" version to allow to compile a version of the program that uses a parallel foreach (an N Body simulator)

Lack of a preprocessor does not imply lack of conditional compilation:

http://dlang.org/version.html

The constructs are simply built into the language.

This has considerable benefits: you can use e.g. `static if` to enable/disable code based on conditions which refer to constants declared in the program (there is no longer a separate namespace for preprocessor defines and program constants), and with CTFE, you can use any expression that can be evaluated during compilation.

The language it's itself his own preprocesor, thanks to CTFE. I think that it is what I love more of D.

Maybe someone with more D experience can chime in, but D has conditional compilation (ie "static if")

http://dlang.org/version.html

In many cases you don't need preprocessor for this even in C++. For example you can detect the availability of system functions using function overloading as described in http://zverovich.net/2015/03/13/reliable-detection-of-strerr...

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