X header like functionality

[Matt Soucy]

On 07/08/2012 05:39 AM, Lukasz wrote:
> On Sunday, 8 July 2012 at 08:05:58 UTC, Mattias wrote:
>> Hi, I spent some time recently learning D. I am curious about the best
>> way to implement something like X-includes in C. I.e. where one use
>> macros that you redefine at the include point.
>>
>> This is indispensable sometimes for keeping code in sync.
>>
>> For example, if we in an include header writes:
>>
>> ---
>> #ifndef X
>> #define X(a, b)
>> #endif
>>
>> X(int, foo)
>>
>> #undef X
>> ---
>>
>> We can then include it as follows (this probably won't compile, but
>> should serve as an illustration):
>>
>> // Define the globals
>> #define X(a, b) a b;
>> #include "blah.inc"
>>
>> struct {char *, void *} myarray[] = {
>> #define X(a, b) {#b, &b} , // C99 allows for comma at the end
>> #include "blah.inc"
>> };
>>
>> The point here is that we can make a single point definition of
>> something which is then later used in multiple locations in order to
>> keep things in sync.
>>
>> So my question is, whether there is some clever way to use mixins and
>> templates that accomplish roughly the same thing of defining a table
>> at one location and then reusing the table at multiple locations for
>> different purposes?
>
> This should do the trick:
>
> alias tuple!("MBlaze",
>               "CppBackend",
>               "MSIL",
>               "CBackend",
>               "Blackfin",
>               "SystemZ",
>               "MSP430",
>               "XCore",
>               "PIC16",
>               "CellSPU",
>               "Mips",
>               "ARM",
>               "Alpha",
>               "PowerPC",
>               "Sparc",
>               "X86") Targets;
>
> string TARGETS(string prefix, string postfix)
> {
>      string ret = "";
>      foreach(target; Targets)
>      {
>          ret = ret ~ prefix ~ target ~ postfix;
>      }
>      return ret;
> }
>
> mixin(TARGETS("void LLVMInitialize", "TargetInfo();\n"));
> mixin(TARGETS("void LLVMInitialize", "Target();\n"));
> mixin(TARGETS("void LLVMInitialize", "TargetMC();\n"));
>
Another thing that is closer to the original idea is to use string 
imports. By using -J instead of -I as an argument to dmd, you can tell 
it to look for string imports within a certain folder. After that, you 
simply:
 >>>import("stuff.inc");
and it gets treated as a string literal.

So, how is this helpful? At this point, you can use mixin, as in
 >>>mixin(import("stuff.inc"));
Or, you could use a CTFE function to mess with the string first, it's up 
to you.

I'm attaching a quick test I whipped up, hopefully it sends...

-Matt Soucy
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X(1);
X(2);
X(3);
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