Hi!

I am trying to port a program I have written earlier to D. My previous versions are in C++ and Python. I was hoping that a D version would be similar in speed to the C++ version, rather than similar to the Python version. But currently it isn't.

Part of the problem may be that I haven't learned the idiomatic way to do things in D. One such thing is perhaps: how do I read large text files in an efficient manner in D?

Currently I have created a little test-program that does the same job as the UNIX-command "wc -lc", i.e. counting the number of lines and characters in a file. The timings I get in different languages are:

D: 15s

C++: 1.1s

Python: 3.7s

Perl: 2.9s

The central loop in my D program looks like:

foreach (line; f.byLine) {

nlines += 1;

nchars += line.length + 1;

}

I have also tried another variant with this inner loop:

char[] line;

while(f.readln(line)) {

nlines += 1;

nchars += line.length;

}

but in both cases this D program is much slower than any of the others in C++/Python/Perl. I don't understand what can cause this dramatic difference to C++, and a factor 4 to Python. My D programs are built with DMD 2.067.1 on MacOS Yosemite, using the flags "-O -release".

Is there something I can do to make the program run faster, and still be "idiomatic D"?

(I append the whole program for reference)

Regards,

/Johan Holmberg

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import std.stdio;

import std.file;

void main(string[] argv) {

foreach (fname; argv[1..$]) {

auto f = File(fname);

int nlines = 0;

int nchars = 0;

foreach (line; f.byLine) {

nlines += 1;

nchars += line.length + 1;

}

writeln(nlines, "\t", nchars, "\t", fname);

}

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