[Boost-commit] svn:boost r50144 - sandbox/committee/rvalue_ref

Subject: [Boost-commit] svn:boost r50144 - sandbox/committee/rvalue_ref
From: dave_at_[hidden]
Date: 2008-12-05 16:21:29

Author: dave
Date: 2008-12-05 16:21:29 EST (Fri, 05 Dec 2008)
New Revision: 50144
URL: http://svn.boost.org/trac/boost/changeset/50144

Log:
Partial update

Text files modified: 
   sandbox/committee/rvalue_ref/n2812_08-0322_soundness.rst |    91 ++++++++++++++++++++++++++++++++++++++++
   1 files changed, 91 insertions(+), 0 deletions(-)

Modified: sandbox/committee/rvalue_ref/n2812_08-0322_soundness.rst
==============================================================================
--- sandbox/committee/rvalue_ref/n2812_08-0322_soundness.rst	(original)
+++ sandbox/committee/rvalue_ref/n2812_08-0322_soundness.rst	2008-12-05 16:21:29 EST (Fri, 05 Dec 2008)
@@ -1,3 +1,80 @@
+++++++++++++++++++++++
+ New Iterator Concepts
+++++++++++++++++++++++
+
+.. Version 1.25 of this ReStructuredText document is the same as
+   n1550_, the paper accepted by the LWG.
+
+:Author: David Abrahams, Doug Gregor
+:Contact: dave_at_[hidden], doug.gregor_at_[hidden]
+:organization: `BoostPro Computing`_, Apple Computer `Open Systems
+:date: 2008-12-05
+
+:Number: n2812=08-0322
+
+.. _`BoostPro Computing`: http://www.boostpro.com
+
+Outline
+=======
+
+* Description of problem
+* Proposed fix
+* Impact of fix
+* Implementation Experience
+* Pro/con arguments?
+
+Status of This Document
+=======================
+
+Currently aggregating comments from a long discussion thread starting
+Sept. 19 2008 and just trying to make sure all the important material
+is at hand.  We will incorporate this material in the main text next.
+
+Miscellaneous Remarks and Notes
+===============================
+
+I've tried to bold-ify what I think are the essential points below
+
+* Peter 
+  Dimov:
+
+    I think that we don't need idiom 2 [where we want to modify the
+    argument regardless of whether it turns out to be an rvalue] that
+    much. If we're going to change && to not bind to lvalues, the
+    **principled approach would be to omit the &&& at all**. Yes, idiom 2
+    does have its uses, but it also has shown an ability to bite us
+    **(issue 884)**.
+
+    I also note that **making && bind only to rvalues probably settles
+    the question of whether auto&& should apply the deduction rule** -
+    it wouldn't work for lvalues if it did not.
+
+    We'll need some additional wording to **keep std::move working**;
+    it binds an rvalue reference to an lvalue.
+
+    **I find the original motivating example (where the
+    CopyConstructible concept requirement causes the const& overload
+    to be dropped) much better, because it represents neither a
+    mistake nor an oversight.**
+
+    The std::move implementation takes advantage of the fact that T&&
+    can bind to an lvalue t. The binding can be made explicit, via
+    static_cast, but **a blank prohibition could render even that
+    illegal.**
+
+* The first version of the paper mentioned back_insert_iterator and
+  how the simple workaround for a problem prevents using it with
+  initializer lists, something Doug apparently understood.  Worth
+  mentioning?
+
+* There was a vote in LWG to roll all swap functions back to the
+  single (T&,T&) form because of issue 884.  However, for bureaucratic
+  reasons I'm not sure if that vote had any legal force, so we may
+  need to do something about it.
+
+
+-------------------
+
 Synopsis
 ========
 
@@ -33,6 +110,19 @@
 applied when that argument is an unnamed temporary and thus inaccessible and
 invisible to the rest of the program.
 
+.. Annotation:: Thomas Witt
+
+  add a sentence or two explaining the overload and binding
+  behavior. Pointing out that *both* overloads are needed to make it
+  safe. That might not be clear to people not familiar with rvalue
+  references.
+
+  Dave:
+    Technically, only the first overload is needed to make it safe;
+    the second one is needed to make it move.  So I can try to
+    emphasize that the first overload is needed.
+
+
 How Move-Only Types Work
 ========================
 
@@ -130,3 +220,4 @@
 for C++0x to take an rvalue reference first argument would need a second
 overload.  If not, we should revert these operators to their original
 definitions.
+