Re: Feature request : More lightuserdata types

[云风 Cloud Wu <cloudwu@...>]

Flyer31 Test <flyer31@googlemail.com> 于2022年2月22日周二 23:12写道：
>
> But if you connect "normal C userdata" to metatables, you can also do
> this without library, as e. g. described in Roberto's Programming in
> Lua, Caphter 31, "User defined types in C" for this new bitarray type.
>
> Just what you definitely seem to need here is a code in the following form:
>
>    luaL_newmetatable(L, "my-metatable-name");
> ...
>     lua_newuserdata(L, nbytes);
>     luaL_getmetatable(L, "my-metatable-name");
>     lua_setmetatable(L, -2);
>
> ... so this would connect the metatable to the userdata element
> defined with nbytes Bytes... .
>
> This does NOT need any library functions, this is just standard Lua c  code... .
>
> But how would you do this connection in case of lightuserdata element?

Anything in Lua can has a matatable. As the Lua manual says "Tables
and full userdata have individual metatables, although multiple tables
and userdata can share their metatables. Values of all other types
share one single metatable per type; that is, there is one single
metatable for all numbers, one for all strings, etc. "

For lightuserdata :

lua_pushlightuserdata(L, NULL);
luaL_getmetatable(L, "my_lightuserdata_metatable");
lua_setmetatable(L, -2);

But all the lightuserdata share the same one metatable, if more than
one library does this, only one metatable works. If Lua support
subtype of lightuserdata would be better, and then we can do :

lua_pushlightuserdata(L, NULL, "mytype");
luaL_getmetatable(L, "mytype_metatable");
lua_setmetatable(L, -2);

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