The __newindex metamethod
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: The __newindex metamethod
- From: Dirk Laurie <dpl@...>
- Date: 2011年1月10日 21:28:26 +0200
The reference manual states:
--
"newindex": The indexing assignment table[key] = value.
--
The operation can be overridden by redefining __newindex
in the metatable. However, the overriding function is
only invoked when table[key] does not yet exist. Otherwise,
table[key]=value <==> rawset(table,key,value).
This behaviour is documented in the reference manual by the
Lua code for settable_event,
local v = rawget(table, key)
if v ~= nil then rawset(table, key, value); return end
h = metatable(table).__newindex
if h == nil then rawset(table, key, value); return end
which corresponds closely to the C code for luaV_settable in lvm.c.
I can't guess why the overriding function is not always invoked
when available, i.e. simply
h = metatable(table).__newindex
if h == nil then rawset(table, key, value); return end
unless it is because the user is not trusted to call rawset in
the function supplied, which could cause dangling references.
In the meantime, if I want this simpler behaviour, it seems that
I will have to change the code in lvm.c and recompile Lua.
Dirk