RangePosition vs TransparentPosition
Mirco Dotta
---------------
Mirko Stocker
Let me try to answer that: As you know, trees that have a direct
correspondence in the source code have a RangePosition, and compiler-generated
trees have an OffsetPosition. By INV1 in Position.scala, "a tree with an offset
position never contains a child with a range position". The problem is that
there are ASTs that don't have a source-code correspondence but still have
children that are visible in the source. So that's where the
TransparentPositions come into play, for example:
"abc".charAt _
is represented as a Function tree, where the Function, the parameter ValDef
and the Apply all have a TransparentPosition, and the Select(Literal(""),
"charAt") has a RangePosition.
I hope this helps,
Mirko
--
Mirko Stocker | m...@misto.ch
Work: http://ifs.hsr.ch | http://infoq.com
Personal: http://misto.ch | http://twitter.com/m_st
Mirco Dotta
martin odersky
overlap. So If you want to create two Range position trees that do
have subtrees with interleaving range positions, one of them must be a
transparent position.
The doc comment to scala.tools.nsc.util.Position is really required
reading for anyone dealing with positions.
Cheers
- Martin
Mirco Dotta
Mirko is correct. One more point: Trees with range positions may not
overlap. So If you want to create two Range position trees that do
have subtrees with interleaving range positions, one of them must be a
transparent position.
The doc comment to scala.tools.nsc.util.Position is really required
reading for anyone dealing with positions.
Cheers
- Martin
martin odersky
> Mirko is correct. One more point: Trees with range positions may not
> overlap. So If you want to create two Range position trees that do
> have subtrees with interleaving range positions, one of them must be a
> transparent position.
>
>
> I might be failing to understand your point, but it looks like
> a TransparentPosition
> is allowed to break the contract of a RangePosition.
>
> If the above is true, then why TransparentPosition <: RangePosition?
>
> The doc comment to scala.tools.nsc.util.Position is really required
> reading for anyone dealing with positions.
>
>
> I read
> this http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/compiler/scala/tools/nsc/util/Position.html,
> but I can't find the explanation you gave about TransparentPositions.
>
I meant opaque range positions may not overlap, where an opaque range
position is a range position that is not also a transparent range
position. See INV 3 in the doc comment.
Cheers
- Martin
> Cheers
>
> - Martin
>
>
>
> ---------------
> Mirco Dotta
> Typesafe - The software stack for applications that scale
> PSE-D, 1015 Lausanne, Switzerland
> Work: +41 (0)21 691 49 65
> Twitter: @mircodotta
>
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--
Martin Odersky
Prof., EPFL and Chairman, Typesafe
PSED, 1015 Lausanne, Switzerland
Tel. EPFL: +41 21 693 6863
Tel. Typesafe: +41 21 691 4967
