Re: Interesting observation (predicate with std::sort)

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 2 Feb 2010 14:24:39 -0800 (PST)

Message-ID:

<e35966f4-87aa-4c05-8f43-69160995c9b3@19g2000yql.googlegroups.com>

On Feb 2, 7:06 pm, Stephen Howe <sjhoweATdialDOTpipexDOTcom> wrote:

On Tue, 02 Feb 2010 12:58:12 -0500, Victor Bazarov
<v.Abaza...@comAcast.net> wrote:

I am sure I'm not the first one to find this, I just hadn't
run across that behaviour until a few days ago.

Yes I found this out recently. I dont believe the compiler can
inline function pointers (what the function decays to) whereas
it can inline functors. Just about the entire STL runs on
functors so supplying functors is better.

In theory, a compiler can inline anything it knows about. The
problem is that the instantiation type doesn't tell the compiler
which function will be called in the case of a pointer to
function; it does in the case of a functional object.

But I am wondering, what are the benefits to making sure yoru
functor is publically derived from unary_function and
binary_function? Can the compiler and/or library do additional
optimisations because they can infer sometihng on the types?

I am not seeing any mileage but I would like to be convinced
for/against.

It allows your functional object to be combined with other types
defined in <functional>. It has absolutely no effect in
functions like sort.

--
James Kanze