On 02/12/2010 14:18, Bruno Medeiros wrote:
On 20/11/2010 08:07, Andrei Alexandrescu wrote:
TDPL has an example that can be reduced as follows:
void main() {
uint[string] map;
foreach (line; stdin.byLine()) {
++map[line];
}
}
byLine reuses its buffer so it exposes it as char[]. Therefore,
attempting to use map[line] will fail. The program compiled and did the
wrong thing because of a bug.
The challenge is devising a means to make the program compile and work
as expected. Looking up an uint[string] with a char[] should work, and
if the char[] is to be inserted, a copy should be made (via .idup or
to!string). The rule needs to be well defined and reasonably general.
The effect is something like this:
void main() {
uint[string] map;
foreach (line; stdin.byLine()) {
auto p = line in map;
if (p) ++*p;
else map[line.idup] = 1;
}
}
Ideally the programmer would write the simple code (first snippet) and
achieve the semantics of the more complex code (second snippet). Any
ideas?
Andrei
An idea:
import std.conv;
//...
uint[string] map;
foreach (line; stdin.byLine()) {
map.getOrPut(line, 0, to!string) ++;
}
Also, it doesn't use pointers, which I guess may be a bit of an advantage.
--
Bruno Medeiros - Software Engineer
