Is it possible to append to a local buffer without reallocating?

[Steven Schveighoffer]

On 1/11/18 6:21 AM, tipdbmp wrote:
> string push_stuff(char[] buf, int x) {
>      if (x == 1) {
>          buf ~= 'A';
>          buf ~= 'B';
>          buf ~= 'C';
>          return cast(string) buf[0 .. 3];
>      }
>      else {
>          buf ~= 'A';
>          buf ~= 'B';
>          return cast(string) buf[0 .. 2];
>      }
> }
> 
> void foo() {
>      {
>          char[2] buf;
>          string result = push_stuff(buf, 1);
>          assert(buf.ptr != result.ptr);
>      }
> 
>      {
>          char[2] buf;
>          string result = push_stuff(buf, 0);
>          assert(buf.ptr == result.ptr); // <-- this assert fails
>      }
> }
> 

Appender is able to do this:

import std.array;

void main()
{
     char[2] buf;
     auto app = appender(buf[]);
     app.clear; // resets the buffer so it can be used again.
     app ~= 'A';
     app ~= 'B';
     assert(buf[] == "AB");
     assert(app.data.ptr == buf.ptr);
     app ~= 'C';
     assert(app.data.ptr != buf.ptr);
}

-Steve