Simplifying nested ifs with multiple exit points in Scala? - scala

Question

There has to be a better way to do this.. I'm testing for a ray-triangle intersection and my code looks something like this
if(some condition) fail
else {
...
if(some other condition) fail
else {
...
intersection
}
}
with many nested ifs. It's disgusting. I'm doing this not to use any return statements. Is there an alternate control structure I could use here to manage the various method exit points?

Answer 1

You could use for comprehension:
val result: Option[BasicIntersection] = for {
edge1 <- Some(vertices(1) - vertices(0))
edge2 = vertices(2) - vertices(0)
P = ray.v cross edge2
determinant = edge1 dot P
if !(determinant > -Utils.EPSILON && determinant < Utils.EPSILON)
inv_determinant = 1.0/determinant
T = ray.p - vertices(0)
u = (T dot P) * inv_determinant
if !(u < 0 || u > 1)
Q = T cross edge1
v = (ray.v dot Q) * inv_determinant
if !(v < 0 || u + v > 1)
t = (edge2 dot Q) * inv_determinant
if !(t < Utils.EPSILON)
hit = ray.p + ray.v*t
} yield
if (hasUV) {
val d0 = Math.abs((hit - vertices(0)).length)
val d1 = Math.abs((hit - vertices(1)).length)
val d2 = Math.abs((hit - vertices(2)).length)
val uvAvg = (uv(0)*d0 + uv(1)*d1 + uv(2)*d2) / (d0 + d1 + d2)
new BasicIntersection(hit, edge1 cross edge2, t, uvAvg)
} else {
new BasicIntersection(hit, edge1 cross edge2, t)
}
result.getOrElse(new BasicIntersection()) // Your failure case