On 26 August 2013 19:00, Jeffrey Yasskin <jyasskin@google.com> wrote:
The library's running into problems because < is unspecified on
pointers that don't point to the same object. (C++14CD[expr.rel]p4)
Naively, this restriction makes a bit of sense, since we can't give a
particular answer for any two pointers, but it's causing problems for
some generic library components. Specifically:

std::map<T*> works because std::less has a special case for pointers.
([comparisons]p14)

std::map<std::tuple<T*>> gives undefined behavior because
std::less<tuple> uses tuple's operator<, which uses T*'s operator<.

std::map<std::optional<T*>> goes back to defined behavior because we
special-cased optional's operator< to use std::less:
[optional.relops]p4

I have strong reasons to believe we'll see an NB comment proposing std::less
to be specialized for tuple<T*> and containers.