This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++11 status.

### 1522. `conj` specification is now nonsense

Section: 28.4.9 [cmplx.over] Status: C++11 Submitter: P.J. Plauger Opened: 2010-10-14 Last modified: 2016-01-28

Priority: Not Prioritized

View all other issues in [cmplx.over].

View all issues with C++11 status.

Discussion:

In Pittsburgh, we accepted the resolution of library issue 1137, to add a sentence 3 to [cmplx.over]:

> All the specified overloads shall have a return type which is the nested `value_type` of the effectively cast arguments.

This was already true for four of the six functions except `conj` and `proj`. It is not completely unreasonable to make `proj` return the real value only, but the IEC specification does call for an imaginary part of -0 in some circumstances. The people who care about these distinctions really care, and it is required by an international standard.

Making `conj` return just the real part breaks it horribly, however. It is well understood in mathematics that `conj(re + i*im)` is `(re - i*im)`, and it is widely used. The accepted new definition makes `conj` useful only for pure real operations. This botch absolutely must be fixed.

[ 2010 Batavia: The working group concurred with the issue's Proposed Resolution ]

[ Adopted at 2010-11 Batavia ]

Proposed resolution:

Remove the recently added paragraph 3 from [cmplx.over]:

> 3 All the specified overloads shall have a return type which is the nested `value_type` of the effectively cast arguments.