At compile time

[div0]

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bearophile wrote:

> D2 is now able to execute math functions (sin, cos, sqrt, etc) at compile time.
> 
> This little C++ program compiles correctly with G++:
> 
> // C++ code
> #include <math.h>
> #include <stdio.h>
> 
> struct V3 {
>     double x, y, z;
>     V3(const double a, const double b, const double c) : x(a), y(b), z(c) {}
>     V3 operator*(const double d) const { return V3(x * d, y * d, z * d); }
>     V3 norm() const { return *this * (1.0 / sqrt(magsqr())); }
>     double dot(const V3 &v) const { return x * v.x+y * v.y + z * v.z; }
>     double magsqr() const { return dot(*this); }
> };
> 
> const V3 v(V3(-0.5, -0.65, 0.9).norm());
> 
> int main() {
>     printf("%f %f %f\n", v.x, v.y, v.z);
>     return 0;
> }

<snip>

> Do you know why?
> Can the D2 compiler modified/improved to allow this?
> 
> Bye and thank you,
> bearophile

Not really relevant to the compile time issue but, your d2 code should be:

import std.math;
import std.stdio;

struct V3 {
    double x, y, z;

	this(double _x, double _y, double _z) {
		x = _x;
		y = _y;
		z = _z;
	}
    V3 opMul(double d) const	{ return V3(x * d, y * d, z * d); }
    V3 norm() const 		{ return this * (1.0 / sqrt(this.magsqr())); }
    double dot(ref V3 v) const	{ return x * v.x+y * v.y + z * v.z; }
    double magsqr()	const		{ return dot(this); }
}

const V3 v;

static this() {
	v = V3(1.0, 2.0, 3.0).norm();
}

int main() {
    writefln("%f %f %f", v.x, v.y, v.z);
    writefln("%f", v.magsqr());
    return 0;
}

This produces identical behavior to the c++ example.

As Jarrett said, in c++ you have hidden runtime initialisation,
which is made explicit in D.

Having it work at compile time would be sweet.

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
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