default metatable
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- Subject: default metatable
- From: <temp212@...>
- Date: 2017年6月29日 20:09:13 +0700
Hello,
I would like to have a "Mathematica style" table arthmetics in
Lua.
it is ok to have it implemented in Lua, something like:
local function ar_func (o1, o2, op)
local o = {};
if type(o1) == "table" and type(o2) == "table" then
if #o1 == #o2 then
for i = 1, #o1 do o[i] = op(o1[i], o2[i]) end
return o
end
elseif type(o1) == "table" and type(o2) == "number" then
for i = 1, #o1 do o[i] = op(o1[i], o2) end
return o
elseif type(o1) == "number" and type(o2) == "table" then
for i = 1, #o2 do o[i] = op(o1, o2[i]) end
return o
end
return nil
end
table.default_metatable = {}
table.default_metatable.__add = function (t1,t2) return
ar_func(t1,t2, function (o1,o2) return o1+o2 end) end
table.default_metatable.__mul = function (t1,t2) return
ar_func(t1,t2, function (o1,o2) return o1*o2 end) end
table.default_metatable.__sub = function (t1,t2) return
ar_func(t1,t2, function (o1,o2) return o1-o2 end) end
table.default_metatable.__div = function (t1,t2) return
ar_func(t1,t2, function (o1,o2) return o1/o2 end) end
table.default_metatable.__pow = function (t1,t2) return
ar_func(t1,t2, function (o1,o2) return o1^o2 end) end
table.default_metatable.__unm = function (t1 ) return
ar_func(t1,t1, function (o1,o2) return -o1 end) end
BUT, the problem is there is no way to set it as metatable to
newly created tables automatically, to make code like {x,y,z}
* {1,0,1} + 5 working.
I made it the ugly way, by modifing OP_NEWTABLE in lvm.c:
void luaV_execute (lua_State *L) {
...
vmcase(OP_NEWTABLE) {
Table *t = luaH_new(L);
//+++++++++++++++
if (NULL == t->metatable){
if (LUA_TTABLE == lua_getglobal(L, "table")){
if (LUA_TTABLE == lua_getfield(L, -1,
"default_metatable")){
t->metatable = hvalue(L->top - 1);
}
lua_pop(L,1);
}
lua_pop(L,1);
}
//+++++++++++++++
...
Currently there are "per type" metatables for all the other
types: numbers, strings.
Is it possible to add one more for the table type, which would
be set as metatable for new tables by default?