• arandomonlooker (24/24) Oct 29 2022 Hello, i'm a beginner to the D programming language that has
• =?UTF-8?Q?Ali_=c3=87ehreli?= (23/27) Oct 29 2022 Although you need that function only at compile time, it is an ordinary
• arandomonlooker (2/8) Oct 29 2022 Thank you, Ali.

arandomonlooker <pnkjkoiftqhgbpzfqi tmmcv.net> writes:

Hello, i'm a beginner to the D programming language that has 
posted many times for simple questions and code errors.
I have written a function that manipulates D code (passed through 
a q{...} block) and returns it to be compiled into the program by 
a mixin.
The problem is that i need to do so in -betterC mode, and for 
example, this code does not compile, giving an error that array 
concatenation of two strings at CTFE is not possible without the 
GC:

```d
string exampleCTFE(string a, string b) {
     return a ~ b;
}
enum example = exampleCTFE("A", "BCDE");
int main() {
     import core.stdc.stdio;
     example.puts;
     return 0;
}
```

Why it complains about the GC if it's a CTFE expression that is 
built at compile time? There is an alternative that works in 
-betterC mode?
Thanks in advance.

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 10/29/22 20:41, arandomonlooker wrote:

 string exampleCTFE(string a, string b) {
      return a ~ b;
 }

Although you need that function only at compile time, it is an ordinary 
function that could be called at run time as well. The function needs GC 
for that concatenation in the general case.

One way of solving your issue would be to change the function to a 
function template and pass the strings as template parameters 
(compile-time parameters):

string exampleCTFE(string a, string b)() {
     return a ~ b;
}

which would require explicit function template instantiation:

enum example = exampleCTFE!("A", "BCDE");

which would cause code bloat because exampleCTFE would be instantiated 
for every string combination that was used. For example, the following 
two uses would require two separate instantiations:

enum example1 = exampleCTFE!("A", "BCDE");
enum example2 = exampleCTFE!("A", "BCDEX");

 int main() {

I think you also need to specify main() as extern(C):

extern (C)
int main() {
   // ...
}

Ali

arandomonlooker <pnkjkoiftqhgbpzfqi tmmcv.net> writes:

On Sunday, 30 October 2022 at 04:14:17 UTC, Ali Çehreli wrote:
 On 10/29/22 20:41, arandomonlooker wrote:

 [...]

 Although you need that function only at compile time, it is an 
 ordinary function that could be called at run time as well. The 
 function needs GC for that concatenation in the general case.

 [...]

Thank you, Ali.