version and debug statements

[Walter Bright]

Anders F Björklund wrote:
> I'm still naively hoping for both of "version (Unix)"

DMD supports Windows and Linux; Unix is neither. For a compiler which 
targets the Unix operating system, it should set the Unix version.

> and "version (!Windows)" to be defined and legal in D.

In C and C++, I often see:

	#if !WIN32

when what is really meant is:

	#if linux

i.e. the former is almost always a bug waiting to happen (when someone 
tries to compile for a third operating system). Versions should be "this 
build is for this configuration" rather than "this build is not for that 
configuration."

One can also write:
	version (ThisFeature)
	{
	}
	else
	{
		version = ThatFeature;
	}

...

	version (ThatFeature)
	...

For an example of why D is this way, see the sources to the Hans Boehm 
garbage collector, where the complex thicket of #if's makes it extremely 
difficult to see exactly what is being compiled.