Template question

Markus Dangl danglm at in.tum.de
Fri Oct 6 09:59:08 PDT 2006

>> Although that's perhaps not a real speedup compared to initializing the
>> program with a counter at runtime...
> could you elaborate with an example I can compile,
> at the moment I don't see how to put it in a working app
> thx,
> roel

Here is a full example, it compiles and runs with my DMD 0.168:
module CompileTimeCounter;
import std.stdio;

pragma(msg, "-- This is at compile time");

// Converts an integer i to a string at compile time.
// Needed for pragma(msg).
template itoa(int i)
     static if (i < 10)  const char[] itoa = "0123456789"[i..i+1];
     else const char[] itoa = itoa!(i/10) ~ "0123456789"[i%10];

// A counter that runs at compile time.
template counter(uint max, uint i=0)
     void initialize()
         pragma(msg, itoa!(i));

         static if (i<max)
             counter!(max, i+1).initialize();

// ncounter has to be const, so it is accessible at compile time.
const int ncounter = 10;

int main(char[][]args)
     writefln("-- This is at run time");
     return 0;
As you can see when you're compiling it counts from 0 to 10 (including 
10). When you run the resulting exe file, it will also print the numbers 
from 0 to 10, but this time there isn't a real counter involved, it's 
just like having
in your code. To be exact, each writefln() is wrapped up in a seperate 
function, this is why i think that a counter at compile time isn't 
really efficient.

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