Why does this mixin fail to compile?

[ryuukk_]

On Wednesday, 3 July 2024 at 03:52:41 UTC, Steven Schveighoffer 
wrote:
> On Tuesday, 2 July 2024 at 07:23:42 UTC, ryuukk_ wrote:
>
>> I said it 2 times already, i don't want string concatenation, 
>> i'll benchmark later, but not right now, right now i'm looking 
>> for a functioning code without string concatenation
>
> Your buffer solution works, but you need to put it inside a 
> *function*, not at declaration scope. What you wrote declares 
> *runtime* variables, which wouldn't be usable at compile time 
> (if you got it past the parser, which is where it was failing).
>
> So for instance:
>
> ```d
> mixin template implement()
> {
>     mixin(() {
>         // ctfe new array is basically the same as static array
>         char[] buffer = new char[4096];
>         int pos = 0;
>
>         void append(string str)
>         {
>             buffer[pos .. pos + str.length] = str[];
>             pos += str.length;
>         }
>
>         append("void* ctx;");
>         return buffer[0 .. pos];
>     }());
> }
> ```
>
> And yes, it is faster to do this than appending. But you have 
> to do a *lot* of it to make a huge difference.
>
> -Steve

That's annoying that it couldn't have been more straight 
forward.. but that'll do it for now, it works, thanks