GrayFace wrote:
So far I've read mentions of several use cases, but I don't
understand how exactly it may be useful in them. Here's what I read
about:
1) Obvious usecase: something like Deplhi's 'with'. This is not the
main use case Lua developers targeted, for sure. Inability to call
global functions, a need for additional local variable to call
methods makes this incomplete.
2) Modules. Maybe it's due to the fact that I didn't work with
modules, but I don't see it useful. I don't see a reason for setting
current environment like 'module' does in 5.1 or use of in-end of 5.2
due to the same reason: inability to call global functions.
Generally, I'd prefer to directly write "function P.f() end" instead
of "function f() end" given P is the module table.
2) Modules...
This is the one that I'm playing with atm.
Basically using environments to trap setglobal in class and module
definitions to set up metatables: function definitions become virtual
methods, "types" become attributes, constants become static members...
etc.
It's mainly sugar, but you can get really close to Ruby's class and
module semantics, and still have it look nice:
in module .Acme do
in module .Friendly do
function greet(self, whom) -- instance method (visible on mixin)
print(self.name.." says: Hello "..whom.."!")
end
function static.answer() -- static method (doesn't mixin)
return 42
end
end
answer() -- 42 (static methods visible here)
in class .Person do
name = String -- instance attribute (type checked)
function __init(self, name)
self.name = name -- TypeError if name is not a string
end
end
end
in class .Hacker (Acme.Person) do
import(Acme.Friendly)
function __init(self, name)
super.__init(self, name) -- "super" injected into environ
end
end
local bob = Hacker.new("Roberto")
bob:greet("World") -- "Roberto says: Hello World!"
I've got the above working (by breaking just about every rule:
"module" is no longer a function, but a magic table, and all
primitives have metatables, except for nil).
I appreciate it's not very Lua'esque to everything-is-an-object'ify,
but I think it's pretty cool that you can create new syntax like that
with just the native language features.
-Rich
