In C/C++ we have preprocessor directives (see title of the question). What is the analog of them in D language? And how to detect operating system type (Windows, Linux, Mac OS X, FreeBSD, ...) and processor type (e.g.: 32 or 64 bits) at compile-time?
Update: The best answer is already on dlang.org: http://dlang.org/pretod.html .
D has no preprocessor. Instead it gives powerful compile-time evaluation and introspection capabilities.
Here is a simple list of typical C/C++ to D translations, with links to relevant documents:
C/C++: #ifdef, #ifndef, #else, #elif
D: version [link]
C/C++: #if <condition>
D: static if [link]
C/C++: #define
D: D translation depends on the case.
Simple C/C++ define like #define FOO is translated to D's "version". Example: version = FOO
Code like #define BAR 40 is translated to the following D code: enum BAR 40 or in rare cases you may need to use the alias.
Complex defines like #define GT_CONSTRUCT(depth,scheme,size) \
((depth) | (scheme) | ((size) << GT_SIZE_SHIFT)) are translated into D's templates:
// Template that constructs a graphtype
template GT_CONSTRUCT(uint depth, uint scheme, uint size) {
// notice the name of the const is the same as that of the template
const uint GT_CONSTRUCT = (depth | scheme | (size << GT_SIZE_SHIFT));
}
(Example taken from the D wiki)
C/C++: #undef
D: There is no adequate translation that I know of