Re: Question about Template

[simendsjo]

On Sat, 23 Jun 2012 17:30:01 +0200, Michael <pon...@gmail.com> wrote:

Hello!

I have a little question about templates. I am trying to write a template "timer" that takes a function and times how long the function takes to execute. Something like

   auto time = timer!sort(array);
is equivalent to
   auto start = Clock.currStdTime();
   sort(array);
   auto time = Clock.currStdTime() - time;

except of course that the variable "start" is not created in the former case.

The closest I came to the correct template is
template(alias F) timer {
   auto timer {
     auto start = Clock.currStdTime();
     F();
     return Clock.currStdTime() - time;
   }
}

The problem with the template is I cannot pass any argument into "F". How should I fix this problem? Also, I am not entirely sure why I need to write "alias F" instead of just "F", any explanation would be appreciated.

Thank you guys,
Michael

import std.datetime;
import std.traits;
import std.stdio;

struct TimerResult(T) {
    TickDuration duration;
    T result;
}

auto timer(alias fn, Args...)(Args args) {
    auto sw = StopWatch(AutoStart.yes);
    auto res = fn(args);
    return TimerResult!(typeof(res))(sw.peek, res);
}

T f(T)(T[] arr) {
    import core.thread;
    Thread.sleep(dur!"seconds"(1));
    return arr[0];
}

void main() {
    auto res = timer!f([1,2,3,4]);
    writeln("first elem: ", res.result);
    writeln("time used: ", res.duration.msecs);
}