Reference to a field element to modify it's properties

[marekjg]

Hi, when rewriting snow simulation from mpm88.cpp I've encountered problem when assigning field element to a variable creates a copy instead of reference (particles didn't move). E.x.:

@ti.dataclass
class Particle:
    x: tm.vec2
    v: tm.vec2
particles = Particle.field(shape=(1000))

@ti.kernel
def modify(dt: ti.f32):
    for idx in particles:
        p = particles[idx]
        p.x += dt * p.v # particles[idx].x stays unmodified

It would be nice to have something like

p = ti.reference(particles, idx)

to tell that p will be reference to particles[idx]. I'm not sure how hard it would be though or if it is already possible.