Request assistance converting C's #ifndef to D

[sanjayss via Digitalmars-d-learn]

On Thursday, 12 May 2016 at 22:51:17 UTC, Andrew Edwards wrote:
> The following preprocessor directives are frequently 
> encountered in C code, providing a default constant value where 
> the user of the code has not specified one:
>
> 	#ifndef MIN
> 	#define MIN     99
> 	#endif
>
> 	#ifndef MAX
> 	#define MAX     999
> 	#endif
>
> I'm at a loss at how to properly convert it to D. I've tried 
> the following:
>
> 	enum MIN = 0;
> 	static if(MIN <= 0)
> 	{
> 		MIN = 99;
> 	}
>
> it works as long as the static if is enclosed in a static 
> this(), otherwise the compiler complains:
>
> 	mo.d(493): Error: no identifier for declarator MIN
> 	mo.d(493): Error: declaration expected, not '='
>
> This however, does not feel like the right way to do thinks but 
> I cannot find any documentation that provides an alternative. 
> Is there a better way to do this?
>
> Thanks,
> Andrew

One thing you could try is compile the C code without the 
#ifndef's and see if it compiles without issues. If it does, 
simply use a D enum and don't worry about translating the 
#ifndef's.

(Alternately check the C code to see if there really are 
differing definitions of MIN/MAX -- if there are, then the code 
is already messed up and you need to implement your D code taking 
into consideration the implications of that -- maybe use 
different variable names in each section of the code for the 
MIN/MAX that takes the different MIN/MAX values. I've typically 
seen this kind of ifdef'ing to quick-fix compile issues in new 
code without having to rewrite a whole bunch of existing code or 
code-structure and it is never to have differing values for the 
defines -- if differing values are used with the same name, then 
the code is bad and it's best to cleanup as you migrate to D.)