Re: Let's talk about __call

[Coda Highland <chighland@...>]

On Fri, Jul 22, 2016 at 10:01 AM, Daurnimator <quae@daurnimator.com> wrote:
> On 22 Jul 2016 06:40, "Peter Aronoff" <telemachus@arpinum.org> wrote:
>>
>> Patrick Donnelly <batrick@batbytes.com> wrote:
>> > For some slightly early "It's Friday" discussion, what do you use the
>> > __call metamethod for? Discuss your favorite hacks, strange problems
>> > solved, code golf hole-in-ones, etc.
>>
>> Here’s one that somebody suggestsed for a module of mine. The module is
>> named split, and the primary method is also split. So if you require it in
>> a conventional way, you get this:
>>
>>         local split = require "split"
>>         local record = "foo,bar,bizz,buzz"
>>         local fields = split.split(record)
>>
>> To avoid the redundancy, he suggested packaging the module this way:
>>
>>         return setmetatable({
>>           split      = split;
>>           -- various other methods
>>         },{
>>           __call = function(_, ...)
>>           return split(...)
>>         end
>>         })
>>
>> So now a user can require the module as normal, but call split using the
>> module alone. I didn’t do it at the time—I thought that it was too magic
>> and unnecessary since it’s easy for a user to assign the method to
>> whatever
>> short name they like when they require the module.
>>
>> But now I’m curious: is this pattern common in other Lua modules? I don’t
>> think I’ve seen it, but perhaps I haven’t seen enough.
>>
>> Best, P
>> --
>> We have not been faced with the need to satisfy someone else's
>> requirements, and for this freedom we are grateful.
>>     Dennis Ritchie and Ken Thompson, The UNIX Time-Sharing System
>
>
> I used to often return functions from modules.
> I now return tables, but to keep compatibility I give them a __call
> metamethod.

I'm kinda going the other direction these days -- it's a bad influence
from spending too much time working with npm, but I'm increasingly
having modules return functions instead of objects when there's only a
single function being returned.

/s/ Adam