Problem slicing and indexing DenseMatrix and DenseVector

[absalom_hicks]

Hello,

I cannot understand why the first part in Test::foo works but the second does not.
This also presents a problem since I cannot write even simple functions,
such as Test::bar below.

I would be very grateful for an explanation and workaround to make functions like Test::bar
work.

    import breeze.linalg.DenseMatrix
    import breeze.linalg.DenseVector

    class Test {

        val dim = 3
        val X:DenseMatrix[Double] = DenseMatrix.rand(dim,dim)
        val u:DenseVector[Double] = DenseVector.fill(dim){1.0}

        def foo:Unit = {

            val i=0;
            val row_i:DenseVector[Double] = X(i,::).t  // OK
            val s = u(i)+u(i)                          // OK

            val j:Integer = 0
            val row_j:DenseVector[Double] = X(j,::).t  // does not compile (A)
            val a = u(j)+u(j)                          // does not compile (B)
        }
        def bar(i:Integer):Double = u(i)+u(i)          // does not compile (C)
    }

Compilation errors:

(A) could not find implicit value for parameter canSlice:
breeze.linalg.support.CanSlice2[breeze.linalg.DenseMatrix[Double],Integer,collection.immutable.::.type,Result]
     
not enough arguments for method apply:
(implicit canSlice: breeze.linalg.support.CanSlice2[breeze.linalg.DenseMatrix[Double],Integer,collection.immutable.::.type,Result])
Result in trait TensorLike.
Unspecified value parameter canSlice.
      


(B), (C)

could not find implicit value for parameter canSlice:
breeze.linalg.support.CanSlice[breeze.linalg.DenseVector[Double],Integer,Result]
     
not enough arguments for method apply:
(implicit canSlice: breeze.linalg.support.CanSlice[breeze.linalg.DenseVector[Double],Integer,Result])Result in trait TensorLike.
Unspecified value parameter canSlice.

[David Hall]

Breeze doesn't always do the right thing with type conversions, including autoboxing and even things like Int to Double promotion. It's a structural thing that is hard to fix without adding a lot more code bloat and a lot more classes (and slowing down compile times more)

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