[fpc-pascal] [fpc-devel] Nested function closures

[Michael Van Canneyt]

On Tue, 27 Apr 2021, Ryan Joseph via fpc-pascal wrote:

>
>
>> On Apr 27, 2021, at 9:58 AM, Michael Van Canneyt <michael at freepascal.org> wrote:
>> 
>> 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.
>> 
>> 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.
>
> Maybe we're misunderstanding each other then. I'm responding to Sven when he says:
>
>> 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.e.  all closures will be interface based because there are not enough
> real world use cases to support any alternative.  Which is contrary to
> what you're saying that nested functions/closure will be compatible types.

Why is this contrary ?

As I understand it:

a closure is used for arguments of type 'reference to procedure'.

In delphi, this procedure can be a real method or an anonymous function.

So why should you not be able to use a local function instead of an
anonymous function ?

How the closure is implemented internally is irrelevant from the programmer's point of view. 
As long as the signature is correct, presumably the compiler can figure out what needs to be 
done: create an interface (with all that implies) or not.

Michael.