Am 27.04.2021 um 17:58 schrieb Michael Van Canneyt via fpc-devel:
On Tue, 27 Apr 2021, Ryan Joseph via fpc-devel wrote:
Continued from our discussion at
https://bugs.freepascal.org/view.php?id=24481.
if the compiler devs will allow me as soon as this is finished I
want to allow the existing nested functions functionality to work
with anonymous functions, so at the very least we don't need to
generate the expensive interface based object which often times is
not even needed. At that point we would need to make nested
functions inline-able, which they are currently not. But we're not
there yet so lets not complicated anything by proposing extensions
to a feature that doesn't even exist yet.
Sven replies:
Getting rid of the interface only works in very narrow circumstances
that are so seldom in real world code that it is not worth the effort.
I'm referring to my test I did a few years ago
(https://github.com/graemeg/freepascal/compare/master...genericptr:anon_funcs)
where I say we can use existing nested functions as a closure when
passing is not required. As you can see I already implemented this
quite easily but it is not related to the new forthcoming closures
feature. I did in fact try to replace the interface with a record on
the old closures branch but I ran into many problems I decided it
wasn't the best route.
Indeed there are many times where we don't want a heap allocated
interface you can pass around but rather a simple inline function
pointer like below. Consider this loop is run 60 times a second and
allocating a useless class every time for no gain. This could easily
be 1000*60=60,000 constructions and allocations of a class.
for i := 0 to entities.Count - 1 do
begin
value := entities[i];
value.SortEntities(function(a, b: TEntity): integer
begin
// do stuff
end
);
end;
So anyways what I propose is if a closure is never passed outside of
scope (i.e. temporary) then use anonymous nested functions instead
(like in my GitHub branch). If this is an acceptable approach I will
personally do what is required to get it implemented along side the
real closures.
Wait.
I asked Sven to make sure that nested functions are under ALL
circumstances
usable as closures or can be used instead of anonymous functions.
Pas2js already supports this, and I want FPC and Pas2JS to be
compatible in
this regard.
The compiler will essentially prepare them as if they're anonymous
functions.
So as Sven wrote, you would be duplicating effort, needlessly, since
it has
to work always... If the compiler can decide that the heap interface
is not
needed and optimize it away: so much the better. But I doubt this will be
possible.
In nearly all cases the interface can't be optimized away.
Regards,
Sven
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