remove keywords

[Michel Fortin]

On 2007-12-07 05:47:36 -0500, Walter Bright <newshound1 at digitalmars.com> said:

> So, by limiting the version statement, the idea is to encourage the 
> programmer to think in terms of distinct versions being generated, and 
> then code in terms of those distinct versions - each of those versions 
> having a name.

I've come into a situation where I'll probably have to take the bloat 
from the code and transfer it to the build process because of this 
limitation. Apple's C/C++/Obj-C headers all use the following idiom to 
create single header files adapted to the target version of Mac OS X 
you wish to use:

	#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_3
	// Mac OS X 10.3 specific functions prototypes
	#endif
	#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4
	// Mac OS X 10.4 specific functions prototypes
	#endif
	#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_5
	// Mac OS X 10.5 specific functions prototypes
	#endif

Then you only need to set MAC_OS_X_VERSION_MAX_ALLOWED to the actual 
version number and you instantly have headers limited to the version 
your application is targeting. (Or if you don't you get headers for the 
latest version.)

The only way I see to replicate that in D when converting Apple headers 
is to use:

	version (MAC_OS_X_VERSION_10_3) {
		// Mac OS X 10.3 specific functions prototypes.
	}
	version (MAC_OS_X_VERSION_10_4) {
		// Mac OS X 10.4 specific functions prototypes.
	}
	version (MAC_OS_X_VERSION_10_5) {
		// Mac OS X 10.5 specific functions prototypes.
	}

This is inconvenient (and error prone) because if you're going to 
import a module with these version flags in your program, you then need 
to define when version flags for each previous version of the OS; and 
the number of symbols to define will always go in increasing. If you 
could just write:

	version (MAC_OS_X_VERSION >= 10.3)

it'd make things much easier. Even better would be:

	version (MAC_OS_X_VERSION <= 10.1 && MAC_OS_X_VERSION > 10.4)

to indicate a function added at version 10.1 and removed in 10.4. To do 
that with my current system, it'd read:

	version (MAC_OS_X_VERSION_10_3) { }
	else version (MAC_OS_X_VERSION_10_1) {
		// some functions added in Mac OS X 10.1 but removed in 10.4.
	}

which isn't that clear either.

By the way, I know I could use simply a version number flag and write:

	version (1) { }
	version (2) { }
	version (3) { }

But then it'll prevent anyone from using version numbers for their own 
application when using ported headers.

Now that I'm thinking about it, the simplest solution probably lies in 
using version to declare some constants in a module mimicking 
AvailabilityMacros.h, then using those constants with static ifs.=.

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/