Strange compiler error. Whose bug is that?

[Oleksii Skidan]

Hi,

I get a strange error:

```
λ dub build
Performing "debug" build using D:\d\dmd2\windows\bin\dmd.exe for 
x86.
strange ~master: building configuration "application"...
source\app.d(24,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][0]
source\app.d(25,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][1]
source\app.d(24,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][1]
source\app.d(25,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][2]
source\app.d(24,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][2]
source\app.d(25,18): Error: non-constant expression 
&[Particle(1.00000F, 1.00000F, 1.00000F), Particle(2.00000F, 
2.00000F, 1.00000F), Particle(3.00000F, 3.00000F, 1.00000F)][0]
D:\d\dmd2\windows\bin\dmd.exe failed with exit code 1.
```

when compiling the following code:

```
import std.stdio;

struct Particle {
     float x;
     float y;
     float invMass;

     this(float x, float y)
     {
         this.x = x;
         this.y = y;
         this.invMass = 1f;
     }
}

struct Constraint {
     Particle* x;
     Particle* y;

     float distance;

     this(ref Particle x, ref Particle y)
     {
         this.x = &x;
         this.y = &y;

         auto dx = x.x - y.x;
         auto dy = x.y - y.y;

         import std.math;
         this.distance = sqrt(dx*dx + dy*dy);
     }
}

interface Body {
     void tick();
}

class Triangle : Body {

     Particle[3] particles = [
         Particle(1, 1),
         Particle(2, 2),
         Particle(3, 3)
     ];

     Constraint[3] constraints;

     this()
     {
         constraints[0] = Constraint(particles[0], particles[1]);
         constraints[1] = Constraint(particles[1], particles[2]);
         constraints[2] = Constraint(particles[2], particles[0]);
     }

     void tick()
     {
         particles[0].x += 1;
     }
}

struct Game {
     Triangle player = new Triangle;

     void tick() {
         player.tick();
     }
}

void main()
{
     Game game;
     game.tick();
}
```

Is that my bug (highest probability here) or a compiler bug? I'm 
confused, since the following `main` function compiles 
successfully:

```
void main()
{
     Triangle player = new Triangle;
     player.tick();
}
```

as well as this code:

```

struct Game {
     Triangle player;

     this(Triangle player)
     {
         this.player = player;
     }

     void tick() {
         player.tick();
     }
}

Game makeGame()
{
     return Game(new Triangle);
}

void main()
{
     auto game = makeGame();
     game.tick();
}
```

What's wrong with the first code snippet?

Thanks in advance,
--
Oleksii