Compiletime Table

[D_Learner via Digitalmars-d-learn]

On Thursday, 13 August 2015 at 19:26:12 UTC, Adam D. Ruppe wrote:
> On Thursday, 13 August 2015 at 19:13:55 UTC, D_Learner wrote:
>> I was wondering how I could change the code below such the 
>> `bmBc` is computed at compile time .
>
> It is currently not possible to build an associative array at 
> compile time and keep it as a runtime table due to the 
> implementation.
>
> However, looking at your code, you don't need a full AA... the 
> key is a single char, right?
>
> Do something like this:
>
> int[128] bmBc = calculate(); // ....
>
>
> And then a line like this should work to set it in the 
> calculate function:
>
>     bmBc[pattern[i]] = i-1;
>
>
>
> Adjust this code to fit you:
>
>
> int[128] a = calc();
> enum string pattern = "abc";
>
> int[128] calc() {
>         int[128] a; // local copy to work on as we build
>         a[pattern[0]] = 0;
>         return a; // return the completed table
> }
>
>
>
>
> This works because individual characters have a numeric value. 
> If they are all A-Z, you can easily fit them in a small array 
> and access them even faster than an associative array (doesn't 
> even have to be full size 128 if the only keys are the letters).
>
> And these can be built at CTFE and stored in the program's data 
> segment.

Thanks, the 128 is fine since I was considering the whole ASCII 
character set . I was a bit skeptical of writing the code in that 
manor though since I have to still compare runtime and 
compiletime implementation performance(benchmarks ). That is why 
my code seemed to mimic templating . Maybe the question would 
then be, how do I force this function to be fully executed at 
compiletime and  later make it be executed at runntime ?