Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://cplusplus.github.io/LWG/issue2171 below:

"swappable" undefined for swapping lvalue and rvalue

This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of NAD status.

Section: 16.4.4.3 [swappable.requirements] Status: NAD Submitter: Robert Shearer Opened: 2012-07-24 Last modified: 2016-01-28

Priority: Not Prioritized

View all other issues in [swappable.requirements].

View all issues with NAD status.

Discussion:

Paragraph 16.4.4.3 [swappable.requirements] p4 states:

An rvalue or lvalue t is swappable if and only if t is swappable with any rvalue or lvalue, respectively, of type T.

This paragraph seems to establish two disjoint definitions of "swappable" — one for lvalues and one for rvalues — with neither definition including the case of swapping an rvalue with an lvalue.

[ 2012-10 Portland: Close as NAD ]

The current wording does intentionally specify two families of 'swappable' behaviors, for lvalues and for rvalues, and not for mixed behavior. The need to support rvalues is for types like vector<bool>::reference. Likewise, library types like string provide a swap for values, but not a mixed-mode swap between lvalues and rvalues, which were deliberately removed from C++11 after initally being part of the standard.

Accepting this resolution would break the library specification, as no current library type would meet the new requirements.

Proposed resolution:

This wording is relative to N3376.

Change 16.4.4.3 [swappable.requirements] p4 as indicated:

An rvalue or lvalue t is swappable if and only if t is swappable with any rvalue or lvalue , respectively, of type T.

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4