C#'s conditional attributes

[Andrei Alexandrescu]

Just saw this on reddit:

http://www.reddit.com/r/programming/comments/cocww/little_known_c_feature_conditional_attributes/

and was wondering whether this can be done in D by relying on lazy 
parameters and the inliner. Here's the test bed:

void log(A...)(lazy string format, lazy A objects)
{
}

void main(string args[])
{
     log(args[0] ~ "yah", args ~ args, 42 + args.length);
}

The dependency on args is intended to prevent the optimizer from 
hoisting evaluation to compilation time.

In an ideal world, the compiler should generate lambdas for the three 
expressions, pass them to log(), then inline, figure out there's no 
really use of either lambda, and let them vanish.

Indeed that's quite what happens when compiling with -O -inline 
-release. The generated _Dmain is the same as a baseline with an empty 
main(). Once this is in place, a simple version() selector dispatches to 
either the empty log() above or one that actually logs stuff. Useful to 
know.


Andrei