Perhaps a tangent, but I've found myself using this kind of
construct a good deal:
function apply(o, f, ...)
setfenv(f, o)
return f(...)
end
-- example --
obj = { foo = 4 }
meth = function()
foo = foo + 1 -- no self or upvalue
end
apply(obj, meth)
print(obj.foo) -- 5
Basically I like the idea of being able to refer to table values
implicitly within a function, which may be a 'leftover mindset'
from working in OO languages, may be an aesthetic thing (avoiding
lots of self. elements in frequently used functions), but maybe
also because I enjoy the flexibility that Lua environments offer.
I couldn't say what the potential overhead or possible pitfalls of
this approach are (other than the obvious possibility that obj o
does not have a member foo etc.)
A more careful implementation would be (untested):
function apply(o, f, ...)
local e = getfenv(f)
setfenv(f, o)
local ret = {f(...)}
setfenv(f, e)
return unpack(ret)
end
The apply function could be added to a metatable used by all
object, or even (if efficiency is not a concern) by all tables.
On Mar 15, 2007, at 12:39 PM, Brian Hagerty wrote:
Kein-Hong Man wrote:
Wow, another hot discussion. Sounds like a religious preference.
Well, no offense, but if you can convince Guido van Rossum to do
it first, then maybe I will sit up and pay attention.
You're right, colon-free versus colon-full function definitions is
probably a religious preference. If the choice between a dot-
syntax and a colon-syntax exists, programmers should just choose
what they are most comfortable with (perhaps because they were
used to similar syntax in another language).
I personally would like to see a colon-free and hidden argument
alternative in Lua for object.method calls just for the sake of
elegance in the language. I believe this can be easily done with
an implementation of self that doesn't use the "hidden argument"
implementation pattern that I described in my previous post.
In any case, it's a wish list item that in fact amounts to a
religious choice. -- Call me a hidden argument, colon-atheist!
Cheers,
// Brian
