4 ms·

> D has no need for a preprocessor How does this work, specifically conditional compilation? I have lots of code like this: #if APPLE /* do thing

> 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?

vitaut 12y ago
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-strerror-variants.html http://zverovich.net/2015/03/13/reliable-detection-of-strerr...
kevinnk 12y ago
Maybe someone with more D experience can chime in, but D has conditional compilation (ie "static if") http://dlang.org/version.html http://dlang.org/version.html
WalterBright 12y ago
Check out https://github.com/D-Programming-Language/phobos/blob/master/std/file.d 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 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.
- ridiculous_fish 12y ago
  Thank you for the reply. That's very elegant!
  - deleted 12y ago
    [deleted]
- ape4 12y ago
  Can it do more complex ifdefs - with or's and and's etc?
  - WalterBright 12y ago
    'static if' can - it has full access to the language.
CyberShadow 12y ago
Lack of a preprocessor does not imply lack of conditional compilation: http://dlang.org/version.html 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.
- Zardoz84 12y ago
  The language it's itself his own preprocesor, thanks to CTFE. I think that it is what I love more of D.
Zardoz84 12y ago
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.d 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)

> D has no need for a preprocessor How does this work, specifically conditional compilation? I have lots of code like this: #if __APPLE__ /* do thing

vitaut 12y ago

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-strerror-variants.html http://zverovich.net/2015/03/13/reliable-detection-of-strerr...

kevinnk 12y ago

Maybe someone with more D experience can chime in, but D has conditional compilation (ie "static if") http://dlang.org/version.html http://dlang.org/version.html

WalterBright 12y ago

Check out https://github.com/D-Programming-Language/phobos/blob/master/std/file.d 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 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.

ridiculous_fish 12y ago
Thank you for the reply. That's very elegant!
- deleted 12y ago
  [deleted]
ape4 12y ago
Can it do more complex ifdefs - with or's and and's etc?
- WalterBright 12y ago
  'static if' can - it has full access to the language.

CyberShadow 12y ago

Lack of a preprocessor does not imply lack of conditional compilation: http://dlang.org/version.html 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.

Zardoz84 12y ago
The language it's itself his own preprocesor, thanks to CTFE. I think that it is what I love more of D.

Zardoz84 12y ago

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.d 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)