如何使这种情况更像Scala

Question

I have the following method:

def generateAssociatedImages : List[ImageFileEntry] = {

    if ( this.page > 1 && this.page < this.fileEntry.pageCount ) {
        List( copyWithPage( this.page - 1 ), copyWithPage( this.page + 1 ) )
    } else {
        if ( page == 1 && page != file.fileEntry.pageCount ) {
            List( copyWithPage( this.page + 1 ) )
        } else {
            List( copyWithPage( this.page - 1 ) )
        }
    }

}

But this one looks too much like Java (if I was using Ruby I'd do a switch/case on a range and then do the other comparisons). Is there a more funcional way to do this in Scala?

The behavior is quite simple:

• if input is page 1 and total pages is 3, the output is [2]
• if input is page 2 and total pages is 3, the output is [1,3]
• if input is page 3 and total pages is 3, the output is [2]

I'm looking for an idiomatic solution, I'm still new to Scala.

It would be lovely if I could do something like:

( 1 until 3 ).hasNext( 2 )

Answer 1

Assuming that on a one page, the list of images is empty, you can have the following:

def generateAssociatedImages: List[ImageFileEntry] = {
    val pageCount = fileEntry.pageCount
    page match {
        case `pageCount` if page == 1 => List()
        case `pageCount` => List(copyWithPage(pageCount - 1))
        case 1 => List(copyWithPage(2))
        case x => List(copyWithPage(x - 1), copyWithPage(x + 1))
    }
}

Answer 2

def ifTrue[T](c : Boolean, v : =>T) = if (c) Some(v) else None

def generateAssociatedImages = List(ifTrue(this.page > 1, -1)), ifTrue(this.page < this.fileEntry.pageCount, 1)).flatten.map(d => copyWithPage(this.page + d))

Answer 3

Are you looking for the adjacent pages?

val pages = 1 to this.fileEntry.pageCount

implicit def toNext(r: Range) = new { 
    def next(n: Int) = r.view sliding 2 find (n == _.head) map (_.last)
}

def adjacent(page: Int) = List(pages next page, pages.reverse next page).flatten

def generateAssociatedImages : List[ImageFileEntry] = 
    adjacent(this.page) map copyWithPage

It's a bit of an over-engineering, I admit. But it is elegant. It doesn't work for single-paged ranges either, because of a bug in sliding .