[fpc-devel] Functors

[Blaise at blaise.ru]

On 26.12.2021 11:50, Michael Van Canneyt via fpc-devel wrote:
> Please explain what's the point or benefit of this.

Do you mean "in general", or "specifically to FPC"?

A) In general: I reckon that the article covers the matter quite well; I have nothing to add.
B) Specifically for FPC: it is up to the users to decide whether they find this useful; I am impartial.

Personally for me, specifically for FPC, the points are:
1) A variant of that patch is already a part of the Closures -- it makes sense to expose that to the users and get another feature (Functors) for "half the price";
2) Orthogonality -- I would rather implement a proper feature instead of employing a specific "hack" for a single case (translating an interface reference into a call).

> As I see it, it's just shorthand syntax to allow skipping the name 'Invoke'.
> None of what is shown below cannot be handled by ordinary methods

Well, yes. But, following your reasoning, the same should be said about overloading most of the operators: "why is aC+aD better than aC.Add(aD)"?

> I find the resulting code aC(33) more confusing than anything else

It should be less confusing if you think of aC as a routine (which is the point of Functors). Would aCallback(33) look less confusing?

> I think the idea is overly complicated and can be achieved simply by the mechanism used by default array properties:
>     function Add9(const N: Integer): Integer; default;

That could be an alternative /syntax/ for denoting the special method, but I do not see how that would "uncomplicate" the /idea/. To me, that is exactly the same idea with the same level of complication.

Likewise, conceptually, "default array properties" /is/ "operator []" with a clunkier syntax and a benefit of being able to access such property by name.

> I think the idea of using a fixed member identifier for special purposes is really stupid design.

I would agree in general, but you did see that using the OPERATOR keyword is part of the proposal, right?
"operator Add" is not necessarily worse than "operator +".

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