[fpc-pascal] Are there any drawbacks to "reference to"?
Michael Van Canneyt
michael at freepascal.org
Mon Jun 20 15:30:23 CEST 2022
On Mon, 20 Jun 2022, Sven Barth wrote:
> Michael Van Canneyt <michael at freepascal.org> schrieb am Mo., 20. Juni 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>
>>>>> 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
>>> with enabled optimizations (however in case of a nested function the
>>> 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
>>> 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 ?
> Yes, in your example this is the case, but look at mine again: it's
> unnecessary to create the capture object here and in theory the compiler
> could convert it to an ordinary nested function variable.
My point is that if someone creates an API where he/she uses
"reference to procedure" then the consumer of the API is stuck
with the creation of an interface.
So it's not always a choice whether an interface will be used or not.
My conclusion is then that 'reference to' should be used sparingly in public APIs
as they are (relatively) expensive.
Unless I missed/misunderstod something of course...
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