Re: [RFA v2 1/7] Remove some ui_out-related cleanups from Python

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2017-02-09 16:24, Tom Tromey wrote:
> This patch introduces a bit of infrastructure -- namely, a minimal
> std::optional analogue called gdb::optional, and an RAII template
> class that works like make_cleanup_ui_out_tuple_begin_end or
> make_cleanup_ui_out_list_begin_end -- and then uses these in the
> Python code.  This removes a number of cleanups and generally
> simplifies this code.
>
> std::optional is only available in C++17.  Normally I would have had
> this code check __cplusplus, but my gcc apparently isn't new enough to
> find <optional>, even with -std=c++1z; so, because I could not test
> it, the patch does not do this.

I am curious what are the differences between using an std::optional and 
a std::unique_ptr.  Obviously

  std::optional<Foo> opt;
  std::unique_ptr<Foo> ptr;

  opt.emplace (arg);
  ptr.reset (new Foo (arg));

The obvious one is stack memory allocation for optional and heap for 
unique_ptr, but apart from that, any difference in the functionality?