A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4035

Date: 2014-05-23

Implicit Evaluation of auto Variables and Arguments (revision 1)

by Joel Falcou, Peter Gottschling, Herb Sutter

Excerpt:

Revision to N3748

1. Prioritized syntax changed.

2. Third alternative introduced.

3. Library-based disabling introduced.

4. Some type traits removed.

Altogether, the proposal is a clear simplication to its predecessor.

1 Motivation

Type detection for variables from expressions' return type:

auto x= expr;

has proven high usability. However, it fails to meet most users' expectations and preferences when
proxies or expression templates (ET) are involved, e.g.:

matrix A, B;
// setup A and B
auto C= A  B;

Many people would expect C to be of type matrix as well. Whether C is a matrix depends on the
implementation of operator*. ...