Named arguments reorder effects

[allanrenucci]

def foo(bar: Int, bat: Int) = 1
def p(x: Int) = { println(x); x }

Scala 2.12:

scala> foo(bat = p(1), bar = p(2)) 
1
2

Dotty:

scala> foo(bat = p(1), bar = p(2)) 
2
1

[nicolasstucki]

These get reordered in Applications.Application.reorder.

[nicolasstucki]

Which documents:

/** Re-order arguments to correctly align named arguments */
    def reorder[T >: Untyped](args: List[Trees.Tree[T]]): List[Trees.Tree[T]] = {

      /** @param pnames    The list of parameter names that are missing arguments
       *  @param args      The list of arguments that are not yet passed, or that are waiting to be dropped
       *  @param nameToArg A map from as yet unseen names to named arguments
       *  @param toDrop    A set of names that have already be passed as named arguments
       *
       *  For a well-typed application we have the invariants
       *
       *  1. `(args diff toDrop)` can be reordered to match `pnames`
       *  2. For every `(name -> arg)` in `nameToArg`, `arg` is an element of `args`
       */
 def handleNamed(.....

Which looks to be intentional.

@odersky is this right?

[nicolasstucki]

Here is a nice test case that includes default parameters.

object Test {
  def p(x: Int) = { println(x); x }
  def foo(x1: Int, x2: Int, , x3: Int, x4: Int = p(4), x5: Int = p(5)) = 1
  def main(args: Array[String]) = {
    foo(p(1), p(2), p(3)) // 1 2 3 4 5
    foo(p(1), x2 = p(2), x3 = p(3)) // 1 2 3 4 5
    foo(p(1), x3 = p(3), x2 = p(3)) // 1 3 2 4 5
    foo(p(1), x3 = p(3), x5 = p(5), x2 = p(2)) // 1 3 5 2 4
    foo(p(1), x3 = p(3), x4 = p(4), x2 = p(2)) // 1 3 4 2 5
  }
}

[biboudis]

Third one you mean foo(p(1), x3 = p(3), x2 = p(2)) // 1 3 2 4 5, right @nicolasstucki?

[nicolasstucki]

Yes

[biboudis]

This is my current progress biboudis@36977d3

Interestingly I reached this point

    ../tests/run/t9915 failed
    compiling '../compiler/src/dotty/tools/dotc/ast' in test 'compilePos' failed
    compiling '../compiler/src/dotty/tools/dotc/transform' in test 'compilePos' failed
    compiling '../compiler/src/dotty/tools/dotc/core' in test 'compilePos' failed
    compiling '../compiler/src/dotty/tools/dotc/ast' in test 'testPickling' failed
    compiling '../compiler/src/dotty/tools/dotc' in test 'testPickling' failed
    compiling '../compiler/src/dotty/tools' in test 'testPickling' failed
    compiling '../compiler/src/dotty/tools/dotc/transform' in test 'testPickling' failed
    dotty from dotty1 failed

Any recommendation on how to move forward @nicolasstucki?

[nicolasstucki]

I will have a look.