Re: __method metamethod

[Coda Highland <chighland@...>]

On Fri, Jul 19, 2013 at 3:38 PM, Greg Fitzgerald <garious@gmail.com> wrote:
> I wonder if Lua might consider adding a __method metamethod, which
> could be used for OO programming and as an alternative to the colon
> operator.
>
> For example, if you wanted to do OO programming without using the
> colon syntax using Lua 5.2, you might write:
>
> local funcs = {
>     inc = function(self)
>         self.a = self.a + 1
>         return self
>     end
> }
>
> local function new(t)
>    local o = t or {a = 0}
>    return setmetatable(o, {
>       __index = function(t, k)
>           return function(...) return funcs[k](t, ...) end
>       end
>    })
> end
>
> assert(new().inc().inc().inc().a == 3)
>
>
> This style, when compared to using the colon operator, has the nice
> property that the parentheses are optional.  You can write:
>
> local f = new().inc
> assert(f().a == 1)
>
> But performance here is far worse than using the colon operator.  In
> the assertion above, 3 closures are created, whereas there are zero if
> using the colon operator.
>
> If, however, Lua offered a __method metamethod that matched the syntax
> "t.k(...)", then we could add the following to our metatable:
>
>     __method = function(t, k, ...)
>        return funcs[k](t, ...)
>     end
>
> Like using the colon operator, the following code would create no closures:
>
>     new().inc().inc().inc()
>
> Thoughts?
>
> Thanks,
> Greg
>

My first thought is: What's wrong with the colon operator? What
problem does this suggestion actually solve?

/s/ Adam