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u+gFLZMEQqeHScQ1EGaz6FG4WUQ [at] mail [dot] gmail [dot] com" type="cite"> What's up with the <% operator used in type parameters? Why do I have to do
sealed abstract class ColumnViewPolicy[A <% AnalysisColumn] {

instead of
sealed abstract class ColumnViewPolicy[A <: AnalysisColumn] {
I originally had the latter, but I was getting some type errors that I didn't understand. Something like:

type arguments [A] do not conform to class ColumnViewPolicy's type parameter bounds [A <: org.broadinstitute.toolkit.core.domain.analysis.AnalysisColumn] [error] abstract class LeafColumnViewPolicy[A <: AnalysisColumn] extends ColumnViewPolicy[A]
[error] ^
I googled about an found some references to the <% operator, and tried it, and it fixed my problem. But I sure would like to understand why!
Some of these Scala typing concepts are taking a while to sink in, but it's happening.
(More complete source code for above snippets)
Thanks! -John

Best regards

Norbert Tausch

u+gFLZMEQqeHScQ1EGaz6FG4WUQ [at] mail [dot] gmail [dot] com" type="cite"> What's up with the <% operator used in type parameters? Why do I have to do
sealed abstract class ColumnViewPolicy[A <% AnalysisColumn] {

instead of
sealed abstract class ColumnViewPolicy[A <: AnalysisColumn] {
I originally had the latter, but I was getting some type errors that I didn't understand. Something like:

type arguments [A] do not conform to class ColumnViewPolicy's type parameter bounds [A <: org.broadinstitute.toolkit.core.domain.analysis.AnalysisColumn] [error] abstract class LeafColumnViewPolicy[A <: AnalysisColumn] extends ColumnViewPolicy[A]
[error] ^
I googled about an found some references to the <% operator, and tried it, and it fixed my problem. But I sure would like to understand why!
Some of these Scala typing concepts are taking a while to sink in, but it's happening.
(More complete source code for above snippets)
Thanks! -John

The first one uses a so-called view bound (http://programming-scala.labs.oreilly.com/ch12.html#ViewsAndViewBounds), the latter one an upper bound. View bounds work with additional implicit constructor/method-Arguments (evidence parameters) and are not the thing you want to have.

I don't see why there should be a problem. The following code compiles:
    class AnalysisColumn
    sealed abstract class ColumnViewPolicy[A <: AnalysisColumn]
    abstract class LeafColumnViewPolicy[A <: AnalysisColumn] extends ColumnViewPolicy[A]

Since your first class is sealed, the LeadColumnViewPolicy must be within the same source file: http://www.scala-lang.org/node/123

Best regards

Norbert Tausch

Am 01.07.2011 16:22, schrieb john sullivan:

What's up with the <% operator used in type parameters? Why do I have to do
sealed abstract class ColumnViewPolicy[A <% AnalysisColumn] {

instead of
sealed abstract class ColumnViewPolicy[A <: AnalysisColumn] {
I originally had the latter, but I was getting some type errors that I didn't understand. Something like:

type arguments [A] do not conform to class ColumnViewPolicy's type parameter bounds [A <: org.broadinstitute.toolkit.core.domain.analysis.AnalysisColumn] [error] abstract class LeafColumnViewPolicy[A <: AnalysisColumn] extends ColumnViewPolicy[A]
[error] ^
I googled about an found some references to the <% operator, and tried it, and it fixed my problem. But I sure would like to understand why!
Some of these Scala typing concepts are taking a while to sink in, but it's happening.
(More complete source code for above snippets)
Thanks! -John

Hi John,

Another tutorial on it is here:

http://www.artima.com/pins1ed/implicit-conversions-and-parameters.html#21.6

I think of <% as meaning "can be treated as".

Bill

On Fri, Jul 1, 2011 at 7:22 AM, john sullivan wrote:
> What's up with the <% operator used in type parameters? Why do I have to do
> sealed abstract class ColumnViewPolicy[A <% AnalysisColumn] {
> instead of
> sealed abstract class ColumnViewPolicy[A <: AnalysisColumn] {
> I originally had the latter, but I was getting some type errors that I
> didn't understand. Something like:
> type arguments [A] do not conform to class ColumnViewPolicy's type parameter
> bounds [A <: org.broadinstitute.toolkit.core.domain.analysis.AnalysisColumn]
> [error] abstract class LeafColumnViewPolicy[A <: AnalysisColumn] extends
> ColumnViewPolicy[A] [error] ^
> I googled about an found some references to the <% operator, and tried it,
> and it fixed my problem. But I sure would like to understand why!
> Some of these Scala typing concepts are taking a while to sink in, but it's
> happening.
> (More complete source code for above snippets)
> Thanks! -John