I have an idea for Lua that I wish to share. It is
called proxying, or envelopment of values, and is an extension to the
Lua core adding a new type of value: proxy. The purpose of this value
is to encapsulate other values, and it is implemented as such:
typedef struct Proxy {
CommonHeader;
TValue value;
Table *metatable;
} Proxy;
The
base library function 'envelop', using core lua_envelop, can be used to
create a proxy by encapsulating a provided value through an associated
metatable:
proxy = envelop(value, metatable)
This is similar to using an empty table with setmetatable, but the
feature of "envelopment" means the proxied value is passed to
metamethods instead of the proxy. This encapsulation works in the
following way:
prx = envelop(val, meta)
val == self
prx(...) --> meta.__call(self, ...)
val = prx[idx] --> meta.__index(self, idx)
prx[idx] = val --> meta.__newindex(self, idx, val)
That
is, 'val' and not 'prx' is passed to methods of 'meta'. An exception is
garbage collection which will take the finalized proxy as its argument,
to distinguish from the handling of the value. Another exception is
'__metatable' which also applies to the proxy.
A
proxy is a convenient value to use for interfacing, OOP, etc, and
compared to using an empty table it is both more efficient and succinct
than using closures to achieve the same goal.
