[fpc-pascal] Are there any drawbacks to "reference to"?

Michael Van Canneyt michael at freepascal.org
Mon Jun 20 08:04:58 CEST 2022

On Mon, 20 Jun 2022, Sven Barth via fpc-pascal wrote:

> Am 20.06.2022 um 03:37 schrieb Hairy Pixels:
>>> On Jun 19, 2022, at 10:04 PM, Sven Barth <pascaldragon at googlemail.com> 
> wrote:
>>> As you can see the allocation only happens once and not all the time.
>>> What might be worse however is the optimization behavior as in this 
> example the compiler wouldn't optimize the counter variable into a regvar 
> with enabled optimizations (however in case of a nested function the compiler 
> wouldn't do this either if the function isn't inlined).
>> I’m saying if the OUTER method is in a tight loop (Foo in this example) 
> you’re in trouble because it now contains an allocation which is unexpected.
> In that case we're in the same territory as always: ensure that you know 
> what your code does. It's the same reason why adding character by 
> character to a managed String is slower then allocating the string once 
> and then setting the characters. And I think it's very seldom that 
> someone uses a function reference that does not leave the scope of the 
> surrounding function.

Does this not depend on the callback declaration ?

   FuncRef = reference to procedure(a : integer);

Procedure DoSomething(f : FuncRef);

Procedure UseSomething;

   For I:=X to SomeLimit do

Does the declaration of DoSomething (which uses reference to) not 
ensure that an interface is created in UseSomething ? 
Or is the interface only created if you use an anonymous/local function ?

I tried to find your original mail, to look for the answer myself, 
but I don't find it offhand.

It may be a good idea to add the explanation you gave in the announcement 
mail to the wiki (and link to it in the user changes in trunk page)


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