On Friday, 13 June 2014 at 21:08:08 UTC, monarch_dodra wrote:
On Friday, 13 June 2014 at 20:48:16 UTC, Jyxent wrote:
I've been playing around with D and noticed that:
stdin.byLine.writeln
takes ~20 times as long as:
foreach(line; stdin.byLine) writeln(line);
I asked on IRC and this was suggested:
stdin.byLine(KeepTerminator.yes).copy(stdout.lockingTextWriter)
which is slightly faster than the foreach case.
It was suggested that there is something slow about writeln
taking the input range, but I'm not sure I see why. If I
follow the code correctly, formatRange in std.format will
eventually be called and iterate over the range.
Because:
stdin.byLine.writeln
and
foreach(line; stdin.byLine) writeln(line);
Don't produce the same output. One prints a range that contains
strings, whereas the second repeatedly prints strings.
Given this input:
line 1
line 2
Yo!
Then "stdin.byLine.writeln" will produce this string:
["line 1", "line\t2", "Yo!"]
So that's the extra overhead which is slowing you down, because
*each* character needs to be individually parsed, and
potentially escaped (eg: "\t").
The "copy" option is the same as the foreach one, since each
string is individually passed to the writeln, which doesn't
parse your string. The "lockingTextWriter" is just sugar to
squeeze out extra speed.
Hah. You're right. I had seen writeln being used this way and
just assumed that it printed every line, without looking at the
output too closely.
Thanks for clearing that up.
