Re: [scala] vector math parameterized class in scala

Take a look at Scala 2.8's Numeric trait:

http://lampsvn.epfl.ch/trac/scala/browser/scala/trunk/src/library/scala/Numeric.scala

--j

On Tue, Jul 7, 2009 at 5:56 PM, Jonathan Bachrach <jrb@...> wrote:

i see.  that's unfortunate.  how would you recommend writing a vector math parameterized class in scala then (short of actually copying the code)?

On Jul 7, 2009, at 3:50 PM, Marcelo Fukushima wrote:

i think the problem is that Number does not define '+' and '*' methods
- and all the compiler knows about your T is that its a Number
(java.lang.Number)


On Tue, Jul 7, 2009 at 7:40 PM, Jonathan Bachrach<jrb@...> wrote:

i'm trying to define a vector math class using parameterized classes in
scala and am having trouble.  here's an abbreviated version of what i wrote:
class Vec3[T <: Number] (xa: T, ya: T, za: T) {
 val x: T = xa; val y: T = ya; val z: T = za
 def + (o: Vec3[T]): Vec3[T] = new Vec3(x + o.x, y + o.y, z + o.z)
 def * (s: T): Vec3[T] = new Vec3(x * s, y * s, z * s)
 def len (): T = x + y + z
 def == (o: Vec3[T]): Boolean = x == o.x && y == o.y && z == o.z
 def < (o: Vec3[T]): Boolean = x < o.x && y < o.y && z < o.z
}
and here's what scalac says:
rala-692> scalac vec3.scala
vec3.scala:3: error: type mismatch;
 found   : T
 required: String
 def + (o: Vec3[T]): Vec3[T] = new Vec3(x + o.x, y + o.y, z + o.z)
                                              ^
vec3.scala:3: error: type mismatch;
 found   : T
 required: String
 def + (o: Vec3[T]): Vec3[T] = new Vec3(x + o.x, y + o.y, z + o.z)
                                                       ^
vec3.scala:3: error: type mismatch;
 found   : T
 required: String
 def + (o: Vec3[T]): Vec3[T] = new Vec3(x + o.x, y + o.y, z + o.z)
                                                                ^
vec3.scala:4: error: value * is not a member of T
 def * (s: T): Vec3[T] = new Vec3(x * s, y * s, z * s)
                                    ^
vec3.scala:4: error: value * is not a member of T
 def * (s: T): Vec3[T] = new Vec3(x * s, y * s, z * s)
                                           ^
vec3.scala:4: error: value * is not a member of T
 def * (s: T): Vec3[T] = new Vec3(x * s, y * s, z * s)
                                                  ^
vec3.scala:5: error: type mismatch;
 found   : T
 required: String
 def len (): T = x + y + z
                     ^
vec3.scala:7: error: value < is not a member of T
 def < (o: Vec3[T]): Boolean = x < o.x && y < o.y && z < o.z
                                 ^
8 errors found
i had added the T <: Number to try to make it so that the + would be
compatible but it still thinks + only works with strings.  i'm not even
completely sure that Number is a real Scala Class.  i'm obviously not
understanding how to write parameterized classes in scala.  any help would
be appreciated.

--
http://mapsdev.blogspot.com/
Marcelo Takeshi Fukushima