Re: How to loop through characters of a string in D language?

[Salih Dincer via Digitalmars-d-learn]

On Monday, 13 December 2021 at 09:36:57 UTC, Ola Fosheim Grøstad 
wrote:
```d
@safe:

string prematureoptimizations(string s, char stripchar) 
@trusted {
    import core.memory;
    immutable uint flags = 
GC.BlkAttr.NO_SCAN|GC.BlkAttr.APPENDABLE;
    char* begin = cast(char*)GC.malloc(s.length+1, flags);
    char* end = begin + 1;
    foreach(c; s) {
        immutable size_t notsemicolon = c != stripchar;
        // hack: avoid conditional by writing semicolon outside 
buffer
        *(end - notsemicolon) = c;
        end += notsemicolon;
    }
    immutable size_t len = end - begin - 1;
    begin = cast(char*)GC.realloc(begin, len, flags);
    return cast(string)begin[0..len];
}
void main() {
    import std.stdio;
    string str = "abc;def;ab";
    writeln(prematureoptimizations(str, ';'));
}
```

It seems faster than algorithms in Phobos. We would love to see 
this in our new Phobos.

```d
enum str = "abc;def;gh";
enum res = "abcdefgh";

void main()
{
  void mallocReplace()
  {
    import core.memory;

    immutable uint flags =
      GC.BlkAttr.NO_SCAN|
      GC.BlkAttr.APPENDABLE;

    char* begin = cast(char*)GC.malloc(str.length+1, flags);
    char* end = begin + 1;

    foreach(c; str)
    {
      immutable size_t f = c != ';';
      *(end - f) = c;
      end += f;
    }
    immutable size_t len = end - begin - 1;
    begin = cast(char*)GC.realloc(begin, len, flags);

    assert(begin[0..len] == res);
  }

  void normalReplace()
  {
    import std.string;

    string result = str.replace(';',"");
    assert(result == res);
  }

  void delegate() t1 = &normalReplace;
  void delegate() t2 = &mallocReplace;

  import std.stdio : writefln;
  import std.datetime.stopwatch : benchmark;

  auto bm = benchmark!(t1, t2)(1_000_000);

  writefln("Replace: %s msecs", bm[0].total!"msecs");
  writefln("Malloc : %s msecs", bm[1].total!"msecs");
}/* Console Out:
Replace: 436 msecs
Malloc : 259 msecs
*/
```