Re: [PATCH] Use string_file::release in some places

[Lancelot SIX <lsix@lancelotsix.com>]

On Fri, Sep 22, 2023 at 01:42:22PM -0700, Keith Seitz via Gdb-patches wrote:
> On Thu, Sep 21, 2023 at 12:42 PM Tom Tromey via Gdb-patches
> <gdb-patches@sourceware.org> wrote:
> >
> > I found a few spots like:
> >
> >     string_file f;
> >     std::string x = f.string ();
> >
> > However, string_file::string returns a 'const std::string &'...  so it
> > seems to me that this must be copying the string (? I find it hard to
> > reason about this in C++).

Hi Tom and Keith,

I think your assessment is correct.  Such case calls the string copy
operator[1] (i.e. `std::string::string (const std::string &)` - plus the
template expansion).

Same goes for the "return f.string ();" cases from a function returning
a std::string.

FWIW, the changes you made seems good to me.
Reviewed-by: Lancelot Six <lancelot.six@amd.com>

> 
> I admit, you now have me doubting everything I thought I remembered
> on this subject! [TODO: reread the standard literature]
> 
> As far as I can tell, your assessment is at least consistent with what is
> done elsewhere, e.g., location.c, ada-lang,c, and just about everywhere
> else except the two locations you've identified in this patch.
> 
> Would symtab.c's symbol_to_info_string and valops.c:incomplete_type_hint
> also qualify for similar treatment? They use addition assignment, so maybe
> that alters the analogy?

In those cases, because the += operator is used, there is no move
semantics which can be leveraged[2].  This operator can only be used
with:
- const std::string & (what is currently used)
- char
- const char *
- std::initializer_list<char>

C++17 also adds string_view based option, but in all the cases we copy
the data from the argument.

Best,
Lancelot.
> 
> In any case:
> Reviewed-by: Keith Seitz <keiths@redhat.com>
> 
> Keith
> 

[1] https://en.cppreference.com/w/cpp/language/copy_initialization
[2] https://en.cppreference.com/w/cpp/string/basic_string/operator%2B%3D