> python -m timeit -v -n 10 -s 'import os' 'os.system("dub run --single --force foo.d")'

10 loops, best of 3: 578 msec per loop

> python -m timeit -v -n 10 -s 'import os' 'os.system("rdmd --force foo.d")'

10 loops, best of 3: 730 msec per loop


I used an example from the DLang Tour (see below or http://tour.dlang.io/tour/en/gems/template-meta-programming) and tested with more and the overhead seems to stay there:

== Associative arrays ==

http://tour.dlang.io/tour/en/basics/associative-arrays

rdmd 5 loops, best of 3: 637 msec per loop
dub: 5 loops, best of 3: 584 msec per loop

== Loops ==

http://tour.dlang.io/tour/en/basics/loops

rdmd: 5 loops, best of 3: 488 msec per loop
dub: 5 loops, best of 3: 373 msec per loop


#!/usr/bin/env rdmd
/+ dub.sdl:
name "foo"
+/

import std.traits: isFloatingPoint;
import std.uni: toUpper;
import std.string: format;
import std.stdio: writeln;

/// A Vector that just works for
/// numbers, integers or floating points.
struct Vector3(T)
  if (is(T: real))
{
private:
    T x,y,z;

    /// Generator for getter and setter because
    /// we really hate boiler plate!
    ///
    /// var -> T getVAR() and void setVAR(T)
    mixin template GetterSetter(string var) {
        // Use mixin to construct function
        // names
        mixin("T get%s() const { return %s; }"
          .format(var.toUpper, var));

        mixin("void set%s(T v) { %s = v; }"
          .format(var.toUpper, var));
    }

    // Easily generate our getX, setX etc.
    // functions with a mixin template.
    mixin GetterSetter!"x";
    mixin GetterSetter!"y";
    mixin GetterSetter!"z";

public:
    // We don't allow the dot function
    // for anything but floating points
    static if (isFloatingPoint!T) {
        T dot(Vector3!T rhs) {
            return x*rhs.x + y*rhs.y +
                z*rhs.z;
        }
    }
}

void main()
{
    auto vec = Vector3!double(3,3,3);
    // That doesn't work because of the template
    // constraint!
    // Vector3!string illegal;

    auto vec2 = Vector3!double(4,4,4);
    writeln("vec dot vec2 = ", vec.dot(vec2));

    auto vecInt = Vector3!int(1,2,3);
    // doesn't have the function dot because
    // we statically enabled it only for float's
    // vecInt.dot(Vector3!int(0,0,0));

    // generated getter and setters!
    vecInt.setX(3);
    vecInt.setZ(1);
    writeln(vecInt.getX, ",",
      vecInt.getY, ",", vecInt.getZ);
}