[fpc-pascal] Re: Delphi's anonymous functions in Free Pascal

[Alexander Shishkin]

05.11.2011 22:42, Bernd пишет:
> 2011/10/25<michael.vancanneyt at wisa.be>:
>
>>> targethread.queue(
>>>   procedure(targetobject:ttargetobject;a:integer;b:someobject;c:string)
>>>              begin
>>>                targetobject.destinationprocedure(a,b,c);
>>>              end;
>>>
>>> Note how common this looks compared to the original.
>>
>> One point is that you could do the above with a local (and named) procedure
>> as well, and still have all the context. At the very least you would not be
>> raping pascal's readability by putting a
>> complete procedure declaration inside a code block.
>
> How would you preserve the context without finding some place
> somewhere (on the heap) to store the current values of a, b, and c?
>
>
> The natural alternative to a closure if you don't have them in an OO
> language is instead of passing a closure you pass an object (this
> pattern is called Functor). The object contains the function along
> with some state. Of course in a static language this involves a lot of
> boiler plate to define the needed classes with their methods (one
> class definition for every different closure) but once you have done
> this you can use it like the closure in the above example and its
> usage is totally readable:
>
> targetthread.queue(TMyFunctor.Create(targetobject, a, b, c));
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>
>
But modern trend is to add closures into OO languages, because code 
become more laconic.