A debug class has started

[forkit]

On Monday, 13 December 2021 at 20:28:26 UTC, H. S. Teoh wrote:
> On Mon, Dec 13, 2021 at 08:04:24PM +0000, forkit via 
> Digitalmars-d-learn wrote:
>> On Monday, 13 December 2021 at 12:06:53 UTC, WebFreak001 wrote:
>> > 
>> > You should really use `.dup` if you want to mutate your 
>> > string. (You would need to duplicate anyway if you don't 
>> > want an unsafe cast)
>> 
>> (this produces an unpredictable result??)
>> char* w = cast(char*)str.dup;
>
> Shouldn't you be using:
>
> 	char* w = str.dup.ptr;
>
> instead??
>
>
> T

so here are all the possible options I've tried. only 2 of these 
actually produce the expected result.

// ------
module test;

import std : writeln, writefln;
import std.conv : to;

import core.stdc.string : strdup;
import std.string : toStringz;

void main()
{
     string str = "abc;def;ab";

     //char* w = cast(char*)str; // NOPE! A string constant is 
immutable, so expect undefined behaviour.

     char* w = strdup(cast(char*)str); // ok
     //char* w = cast(char*)str.toStringz; // also ok

     // all these below result in an extra character from 
'somewhere' appearing in the writeln output
     //char* w = cast(char*)str.dup; // nope
     //char* w = str.dup.ptr; // nope
     //char* w = &dup(cast(const(char)[])str)[0]; // nope

     writeln(replaceChar(w, str.length, ';', 'X'));
}

immutable(char)[] replaceChar(char* str, ulong len, char ch1, 
char ch2)
{
     for (ulong i = 0; i < len; i++)
     {
         if (str[i] == ch1)
         {
             writefln("Found %c at str[%d]", ch1, i); // fine
             str[i] = ch2;
         }
     }
     return to!(immutable(char)[])(str);
}
// ----------------