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On 2023-02-01 23:43, game frog wrote:
static TValue *index2value (lua_State *L, int idx) { ............. else if (!ispseudo(idx)) { /* negative index */api_check(L, idx != 0 && -idx <= L->top - (ci->func + 1), "invalid index");return s2v(L->top + idx); } ............. } Hi, I have some questions~~ When executing 'else if(!ispseudo(idx)', I found this comment /* negative index */ If 'idx' equals 0 is also a negative index？
The first branch in index2value handles common indexes (positive), then the branch you showed handles the negative indexes. But all pseudo-indexes like LUA_REGISTRYINDEX are negative, so the second branch is executed when the index is neither a positive one nor a pesudo one. But 0 is never a valid index, so the following api_check() handles that.
As the comment says, the second branch does handle negative indexes given by the user, rather pseudo ones defined by Lua itself.
-- Ziyao