hello,

i am trying something like that:

char[] foo(int level, char[] msg)
{
    static c = toString(level);
    return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
}


int main(char[][] args)
{
   mixin(foo(100, "Test"));
   return 1;
}

but gdmd complaints that toString() cannot be evaluated at compile time. is there a way to convert the int to char at compile time?

regards,
Hendrik

Reply to Hendrik,

> hello,
> 
> i am trying something like that:
> 
> char[] foo(int level, char[] msg)
> {
> static c = toString(level);
> return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
> }
> int main(char[][] args)
> {
> mixin(foo(100, "Test"));
> return 1;
> }
> but gdmd complaints that toString() cannot be evaluated at compile
> time. is there a way to convert the int to char at compile time?
> 
> regards,
> Hendrik


Don Clugston's decimaldigit and itoa, see http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d

template decimalDigit(int n)
{
 const char[] decimalDigit = "0123456789"[n..n+1];
} 

template itoa(long n)
{    static if (n < 0)
    const char[] itoa = "-" ~ itoa!(-n);   else static if (n < 10)
    const char[] itoa = decimalDigit!(n);  else
    const char[] itoa = itoa!(n/10L) ~ decimalDigit!(n%10L); }

BCS wrote:
> Reply to Hendrik,
> 
>> hello,
>>
>> i am trying something like that:
>>
>> char[] foo(int level, char[] msg)
>> {
>> static c = toString(level);
>> return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
>> }
>> int main(char[][] args)
>> {
>> mixin(foo(100, "Test"));
>> return 1;
>> }
>> but gdmd complaints that toString() cannot be evaluated at compile
>> time. is there a way to convert the int to char at compile time?
> 
> 
> Don Clugston's decimaldigit and itoa, see http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d


this doesn't work for variables like "level", just with directly wrote numbers.

char[] foo(int level, char[] msg)
{
    char[] c = itoa!(level); //does not work
    char[] c = itoa!(100);   //does work
}

is there no chance, to get this variable value converted?

Hendrik Renken wrote:
> BCS wrote:
>> Reply to Hendrik,
>>
>>> i am trying something like that:
>>>
>>> char[] foo(int level, char[] msg)
>>> {
>>> static c = toString(level);

You can't make it static, since parameters aren't known when the function is compiled. Remember the function is also compiled for regular run-time use. It needs to make sense as such.
Also, std.string.toString(int) unfortunately isn't compile-time executable.

>>> return "writefln(\"%d: %s\""~ c ~", \"" ~ msg ~ "\");";
>>> }
>>> int main(char[][] args)
>>> {
>>> mixin(foo(100, "Test"));
>>> return 1;
>>> }
>>> but gdmd complaints that toString() cannot be evaluated at compile
>>> time. is there a way to convert the int to char at compile time?

Yes, see below

>> Don Clugston's decimaldigit and itoa, see http://trac.dsource.org/projects/ddl/browser/trunk/meta/conv.d

Doesn't work for CTFE parameters.

> this doesn't work for variables like "level", just with directly wrote numbers.
> 
> char[] foo(int level, char[] msg)
> {
>     char[] c = itoa!(level); //does not work
>     char[] c = itoa!(100);   //does work
> }
> 
> is there no chance, to get this variable value converted?

---
import std.stdio;

char[] ctfe_itoa(int value) {
	if (value < 0) return "-" ~ ctfe_itoa(-value);
	if (value < 10) return "0123456789"[value .. value+1];
	return ctfe_itoa(value / 10) ~ ctfe_itoa(value % 10);
}

char[] foo(int level, char[] msg)
{
    auto c = ctfe_itoa(level);
    return "writefln(\"%d: %s\","~ c ~", \"" ~ msg ~ "\");";
}

int main(char[][] args)
{
   pragma(msg, foo(42u, "The answer"));
   pragma(msg, foo(int.max, "int.max"));
   mixin(foo(100, "Test"));
   return 1;
}
---

I originally wrote that function to be more efficient (so it could also reasonably be used at runtime) by using a stack-based buffer and returning buffer.dup, without any recursion. Unfortunately CTFE didn't like it :(.
This version will of course still work at runtime, but will perform way too many allocations for a function like this. (I'm not sure if this will be a problem at compile time).

Hendrik Renken wrote:

> but gdmd complaints that toString() cannot be evaluated at compile time. is there a way to convert the int to char at compile time?


std.metastrings has a couple of ways of doing this.

torhu wrote:
> Hendrik Renken wrote:
> 
>> but gdmd complaints that toString() cannot be evaluated at compile time. is there a way to convert the int to char at compile time?
> 
> 
> std.metastrings has a couple of ways of doing this.

just for the records: with std.metastrings i am running in the same problems having with DDL.

the ctfe_itoa function from Frits van Bommel works great. Thanks again.


another little problem/maybe-bug i ran into:
since i currently only have defined int values for "level", i use a switch-Statement to get propper String representations.

const int CORE = 100;

char[] foo(int level, char[] msg)
{
    char[] name;
    switch(level)
    {
	case CORE:
		name = "CORE"; /******* important line ********/

		break;
	default:
		name = "TEST";
	}
    return "writefln(\"%s: %s\", "~ name ~", \"" ~ msg ~ "\");";
}


int main(char[][] args)
{
   mixin(foo(CORE, "Testmsg"));
   return 1;
}


using
name = "CORE";
writes to the console

100: Testmsg


using
name = "\"CORE\"";
gives me what i want

CORE: Testmsg

shouldnt it also work with "CORE"? or am i missing something here?

regards
Hendrik

--------8< snip code 8<----------
> 
> using
> name = "CORE";
> writes to the console
> 
> 100: Testmsg
> 
> 
> using
> name = "\"CORE\"";
> gives me what i want
> 
> CORE: Testmsg
> 
> shouldnt it also work with "CORE"? or am i missing something here?

sorry for bothering, answered the question myself.

Code:
"writefln(\"%s: %s\", "~ name ~", \"" ~ msg ~ "\");"


using name = "CORE";
gives us the line
"writefln(\"%s: %s\", CORE, "Testmsg");"

note: around ~msg~ i inserted " with \"

so this is not "CORE", instead is uses the defined int variable, which has (of course) the value 100. giving

100: Testmsg