Boost C++ Libraries: Ticket #12788: optional 1.63 no longer can be initialized from ''

piotrwn1@… — Mon, 30 Jan 2017 13:54:01 GMT

To clarify: compiled with gcc5.3 with -std=c++14

piotrwn1@… — Mon, 30 Jan 2017 15:44:04 GMT

Demo: http://melpon.org/wandbox/permlink/hwZZLl23nMcb3bs4

rschiele@… — Thu, 02 Feb 2017 13:31:07 GMT

Note that you can get the old behavior back by defining BOOST_NO_CXX11_UNIFIED_INITIALIZATION_SYNTAX for your code.

owner, status changed

akrzemi1 — Fri, 24 Feb 2017 13:23:10 GMT

owner changed from Fernando Cacciola to akrzemi1
status new → assigned

status changed; cc, resolution set

akrzemi1 — Fri, 24 Feb 2017 13:37:41 GMT

cc akrzemi1 added
status assigned → closed
resolution → invalid

This breakage is intentional.

In fact the previous behavior was inconsistent with std::optional and error-prone. Braces should deduce type optional<T>, not to T. For more details of why it was confusing, see here:

http://stackoverflow.com/questions/40391244/difference-between-boost-optional-and-stdexperimental-optional-assignment/40677193#40677193

Now the following puts the optional into no-value state:

boost::optional<S> so;
so = {};

Just like std::optional.

piotrwn1@… — Sun, 26 Feb 2017 13:09:37 GMT

Well, the OP problem was not with empty braces.

piotrwn1@… — Mon, 27 Feb 2017 11:43:03 GMT

This is real problem, please do not close.

See this code:

#include <boost/optional.hpp>
#include <optional>
#include <iostream>
#define PRN(a) std::cout << #a "\n";
#define DEF(a, r) a { PRN(a); r }
struct Verbose {
    DEF(Verbose(int,double),)
    DEF(Verbose(),)
    DEF(~Verbose(),)
    DEF(Verbose(const Verbose&),)
    DEF(Verbose(Verbose&&),)
    DEF(Verbose& operator = (const Verbose&), return *this;)
    DEF(Verbose& operator = (Verbose&&), return *this;)
};
using vbo = boost::optional<Verbose>;
using vso = std::optional<Verbose>;
int main() {
    vbo bo;
    vso so;
    bo = {1,1.1}; // works for boost1.62, not for boost.1.63
    so = {1,1.1}; // works for std::optional
}

Link do demo: http://melpon.org/wandbox/permlink/wDvuR7T9b7bI5fHq

status changed; resolution deleted

piotrwn1@… — Mon, 27 Feb 2017 11:44:25 GMT

status closed → reopened
resolution invalid

Jürgen Hunold — Fri, 07 Apr 2017 07:50:03 GMT

Create an auto test from the example

See https://github.com/boostorg/optional/pull/28